<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://www.alx-inc.com/role/BasisOfPresentation" xlink:href="alx-20200630.xsd#BasisOfPresentation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/BasisOfPresentationAdditionalInformationDetail" xlink:href="alx-20200630.xsd#BasisOfPresentationAdditionalInformationDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/BasisOfPresentationPolicies" xlink:href="alx-20200630.xsd#BasisOfPresentationPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/CommitmentsAndContingencies" xlink:href="alx-20200630.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/CommitmentsAndContingenciesAdditionalInformationDetail" xlink:href="alx-20200630.xsd#CommitmentsAndContingenciesAdditionalInformationDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedBalanceSheetsUnaudited" xlink:href="alx-20200630.xsd#ConsolidatedBalanceSheetsUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedBalanceSheetsUnauditedParenthetical" xlink:href="alx-20200630.xsd#ConsolidatedBalanceSheetsUnauditedParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsOfCashFlowsUnaudited" xlink:href="alx-20200630.xsd#ConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsOfCashFlowsUnauditedParenthetical" xlink:href="alx-20200630.xsd#ConsolidatedStatementsOfCashFlowsUnauditedParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsOfChangesInEquityUnaudited" xlink:href="alx-20200630.xsd#ConsolidatedStatementsOfChangesInEquityUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsOfChangesInEquityUnauditedParenthetical" xlink:href="alx-20200630.xsd#ConsolidatedStatementsOfChangesInEquityUnauditedParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsOfComprehensiveIncomeUnaudited" xlink:href="alx-20200630.xsd#ConsolidatedStatementsOfComprehensiveIncomeUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsOfIncomeUnaudited" xlink:href="alx-20200630.xsd#ConsolidatedStatementsOfIncomeUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsOfIncomeUnauditedParenthetical" xlink:href="alx-20200630.xsd#ConsolidatedStatementsOfIncomeUnauditedParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/Covid19Pandemic" xlink:href="alx-20200630.xsd#Covid19Pandemic" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/Covid19PandemicNarrativeDetails" xlink:href="alx-20200630.xsd#Covid19PandemicNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/DocumentAndEntityInformation" xlink:href="alx-20200630.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/EarningsPerShare" xlink:href="alx-20200630.xsd#EarningsPerShare" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/EarningsPerShareNarrativeDetails" xlink:href="alx-20200630.xsd#EarningsPerShareNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/EarningsPerShareScheduleOfEarningsPerShareBasicAndDilutedDetail" xlink:href="alx-20200630.xsd#EarningsPerShareScheduleOfEarningsPerShareBasicAndDilutedDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/EarningsPerShareTables" xlink:href="alx-20200630.xsd#EarningsPerShareTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/FairValueMeasurements" xlink:href="alx-20200630.xsd#FairValueMeasurements" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/FairValueMeasurementsFinancialAssetsAndLiabilitiesMeasuredAtFairValueDetail" xlink:href="alx-20200630.xsd#FairValueMeasurementsFinancialAssetsAndLiabilitiesMeasuredAtFairValueDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/FairValueMeasurementsFinancialAssetsAndLiabilitiesNotMeasuredAtFairValueDetail" xlink:href="alx-20200630.xsd#FairValueMeasurementsFinancialAssetsAndLiabilitiesNotMeasuredAtFairValueDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/FairValueMeasurementsTables" xlink:href="alx-20200630.xsd#FairValueMeasurementsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/MarketableSecurities" xlink:href="alx-20200630.xsd#MarketableSecurities" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/MarketableSecuritiesAdditionalInformationDetail" xlink:href="alx-20200630.xsd#MarketableSecuritiesAdditionalInformationDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/MortgagesPayable" xlink:href="alx-20200630.xsd#MortgagesPayable" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/MortgagesPayableAdditionalInformationDetail" xlink:href="alx-20200630.xsd#MortgagesPayableAdditionalInformationDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/MortgagesPayableSummaryOfOutstandingMortgagesPayableDetail" xlink:href="alx-20200630.xsd#MortgagesPayableSummaryOfOutstandingMortgagesPayableDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/MortgagesPayableTables" xlink:href="alx-20200630.xsd#MortgagesPayableTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/Organization" xlink:href="alx-20200630.xsd#Organization" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/OrganizationAdditionalInformationDetail" xlink:href="alx-20200630.xsd#OrganizationAdditionalInformationDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/RecentlyIssuedAccountingLiterature" xlink:href="alx-20200630.xsd#RecentlyIssuedAccountingLiterature" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/RelatedPartyTransactions" xlink:href="alx-20200630.xsd#RelatedPartyTransactions" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/RelatedPartyTransactionsAdditionalInformationDetail" xlink:href="alx-20200630.xsd#RelatedPartyTransactionsAdditionalInformationDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/RelatedPartyTransactionsSummaryOfFeesToVornadoDetail" xlink:href="alx-20200630.xsd#RelatedPartyTransactionsSummaryOfFeesToVornadoDetail" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/RelatedPartyTransactionsTables" xlink:href="alx-20200630.xsd#RelatedPartyTransactionsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/RevenueRecognition" xlink:href="alx-20200630.xsd#RevenueRecognition" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/RevenueRecognitionComponentsOfLeaseRevenueDetails" xlink:href="alx-20200630.xsd#RevenueRecognitionComponentsOfLeaseRevenueDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/RevenueRecognitionDisaggregationOfRevenueDetails" xlink:href="alx-20200630.xsd#RevenueRecognitionDisaggregationOfRevenueDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/RevenueRecognitionNarrativeDetails" xlink:href="alx-20200630.xsd#RevenueRecognitionNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/RevenueRecognitionTables" xlink:href="alx-20200630.xsd#RevenueRecognitionTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/StockBasedCompensation" xlink:href="alx-20200630.xsd#StockBasedCompensation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.alx-inc.com/role/StockBasedCompensationAdditionalInformationDetail" xlink:href="alx-20200630.xsd#StockBasedCompensationAdditionalInformationDetail" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/BasisOfPresentation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/BasisOfPresentationAdditionalInformationDetail" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/BasisOfPresentationPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/CommitmentsAndContingenciesAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingenciesLineItems" xlink:label="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingenciesTable" xlink:label="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" xlink:label="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_91B878D69BC5C70E5FA4A5F05198EB0B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:to="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_91B878D69BC5C70E5FA4A5F05198EB0B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeAndTierIdentifierDomain" xlink:label="loc_us-gaap_TypeAndTierIdentifierDomain_1C80671FDC5C910E5A95A5F05199FBD7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_91B878D69BC5C70E5FA4A5F05198EB0B" xlink:to="loc_us-gaap_TypeAndTierIdentifierDomain_1C80671FDC5C910E5A95A5F05199FBD7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeAndTierIdentifierDomain" xlink:label="loc_us-gaap_TypeAndTierIdentifierDomain_1C80671FDC5C910E5A95A5F05199FBD7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_91B878D69BC5C70E5FA4A5F05198EB0B" xlink:to="loc_us-gaap_TypeAndTierIdentifierDomain_1C80671FDC5C910E5A95A5F05199FBD7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GeneralLiabilityMember" xlink:label="loc_us-gaap_GeneralLiabilityMember_1CFAAF3EAB31CB0D6EAFA5F05199174A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeAndTierIdentifierDomain_1C80671FDC5C910E5A95A5F05199FBD7" xlink:to="loc_us-gaap_GeneralLiabilityMember_1CFAAF3EAB31CB0D6EAFA5F05199174A" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_DiseaseCoverageMember" xlink:label="loc_alx_DiseaseCoverageMember_4A3E5A254BD1B90B7CB5A5F051990E27" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeAndTierIdentifierDomain_1C80671FDC5C910E5A95A5F05199FBD7" xlink:to="loc_alx_DiseaseCoverageMember_4A3E5A254BD1B90B7CB5A5F051990E27" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis" xlink:label="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_B24638072894464EC3CBA5F0519A142B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:to="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_B24638072894464EC3CBA5F0519A142B" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_TypesAndTierIdentifierDomain" xlink:label="loc_alx_TypesAndTierIdentifierDomain_FFB003EC4795F51B46A2A5F0519A318B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_B24638072894464EC3CBA5F0519A142B" xlink:to="loc_alx_TypesAndTierIdentifierDomain_FFB003EC4795F51B46A2A5F0519A318B_default" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_TypesAndTierIdentifierDomain" xlink:label="loc_alx_TypesAndTierIdentifierDomain_FFB003EC4795F51B46A2A5F0519A318B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_B24638072894464EC3CBA5F0519A142B" xlink:to="loc_alx_TypesAndTierIdentifierDomain_FFB003EC4795F51B46A2A5F0519A318B" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_AllRiskPropertyAndRentalValueMember" xlink:label="loc_alx_AllRiskPropertyAndRentalValueMember_CD1A5CAE782273B81A46A5F0519A939B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_TypesAndTierIdentifierDomain_FFB003EC4795F51B46A2A5F0519A318B" xlink:to="loc_alx_AllRiskPropertyAndRentalValueMember_CD1A5CAE782273B81A46A5F0519A939B" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_TerrorismCoverageIncludingNbcrMember" xlink:label="loc_alx_TerrorismCoverageIncludingNbcrMember_2071DF20B15F180C1385A5F0519B471E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_TypesAndTierIdentifierDomain_FFB003EC4795F51B46A2A5F0519A318B" xlink:to="loc_alx_TerrorismCoverageIncludingNbcrMember_2071DF20B15F180C1385A5F0519B471E" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_NbcrMember" xlink:label="loc_alx_NbcrMember_0176C70DDC1CD5610B1AA5F0519B9819" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_TypesAndTierIdentifierDomain_FFB003EC4795F51B46A2A5F0519A318B" xlink:to="loc_alx_NbcrMember_0176C70DDC1CD5610B1AA5F0519B9819" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_90BE3346BC3D0C5CF12FA5F0519B3E45" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:to="loc_dei_LegalEntityAxis_90BE3346BC3D0C5CF12FA5F0519B3E45" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_766EE4587EB2E7E5CF97A5F0519B045A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_90BE3346BC3D0C5CF12FA5F0519B3E45" xlink:to="loc_dei_EntityDomain_766EE4587EB2E7E5CF97A5F0519B045A_default" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_766EE4587EB2E7E5CF97A5F0519B045A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_90BE3346BC3D0C5CF12FA5F0519B3E45" xlink:to="loc_dei_EntityDomain_766EE4587EB2E7E5CF97A5F0519B045A" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_FiftyNinthStreetInsuranceCompanyLlcMember" xlink:label="loc_alx_FiftyNinthStreetInsuranceCompanyLlcMember_1ECD535B59D749C0A119A5F0519C10E4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_766EE4587EB2E7E5CF97A5F0519B045A" xlink:to="loc_alx_FiftyNinthStreetInsuranceCompanyLlcMember_1ECD535B59D749C0A119A5F0519C10E4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_StatementScenarioAxis" xlink:label="loc_srt_StatementScenarioAxis_125E08E8382B0468C3A9A5F0519C05A0" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:to="loc_srt_StatementScenarioAxis_125E08E8382B0468C3A9A5F0519C05A0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="loc_srt_ScenarioUnspecifiedDomain_AC2AA5667D86D344AC05A5F0519CA747_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_125E08E8382B0468C3A9A5F0519C05A0" xlink:to="loc_srt_ScenarioUnspecifiedDomain_AC2AA5667D86D344AC05A5F0519CA747_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="loc_srt_ScenarioUnspecifiedDomain_AC2AA5667D86D344AC05A5F0519CA747" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_125E08E8382B0468C3A9A5F0519C05A0" xlink:to="loc_srt_ScenarioUnspecifiedDomain_AC2AA5667D86D344AC05A5F0519CA747" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ScenarioForecastMember" xlink:label="loc_srt_ScenarioForecastMember_10B2630AF3781E890DC7A5F0519C3DBC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_AC2AA5667D86D344AC05A5F0519CA747" xlink:to="loc_srt_ScenarioForecastMember_10B2630AF3781E890DC7A5F0519C3DBC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_4C749646472CE274685CA5F0519DDBE3" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_4C749646472CE274685CA5F0519DDBE3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_99FAE8BC888A065F2B56A5F0519D8BF1_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_4C749646472CE274685CA5F0519DDBE3" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_99FAE8BC888A065F2B56A5F0519D8BF1_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_99FAE8BC888A065F2B56A5F0519D8BF1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_4C749646472CE274685CA5F0519DDBE3" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_99FAE8BC888A065F2B56A5F0519D8BF1" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_TenantOccupantMember" xlink:label="loc_alx_TenantOccupantMember_5415048487FB155A2C98A5F0519D2EB3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_99FAE8BC888A065F2B56A5F0519D8BF1" xlink:to="loc_alx_TenantOccupantMember_5415048487FB155A2C98A5F0519D2EB3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_02D41971AD3401F66BC1A5F0519DE66B" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_02D41971AD3401F66BC1A5F0519DE66B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_622912B1C9BA1B414B97A5F0519E4469_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_02D41971AD3401F66BC1A5F0519DE66B" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_622912B1C9BA1B414B97A5F0519E4469_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_622912B1C9BA1B414B97A5F0519E4469" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_02D41971AD3401F66BC1A5F0519DE66B" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_622912B1C9BA1B414B97A5F0519E4469" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ParamusPropertyMember" xlink:label="loc_alx_ParamusPropertyMember_3B1343E8272B7E758D68A5F0519E32E9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_622912B1C9BA1B414B97A5F0519E4469" xlink:to="loc_alx_ParamusPropertyMember_3B1343E8272B7E758D68A5F0519E32E9" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RegoPark1PropertyMember" xlink:label="loc_alx_RegoPark1PropertyMember_8911AE7E870ABC190811A5F0519E9584" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_622912B1C9BA1B414B97A5F0519E4469" xlink:to="loc_alx_RegoPark1PropertyMember_8911AE7E870ABC190811A5F0519E9584" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RealEstatePropertyOccupantAxis" xlink:label="loc_alx_RealEstatePropertyOccupantAxis_7D97CA18DC11B66AA71AA5F0519F48CB" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:to="loc_alx_RealEstatePropertyOccupantAxis_7D97CA18DC11B66AA71AA5F0519F48CB" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RealEstatePropertyOccupantDomain" xlink:label="loc_alx_RealEstatePropertyOccupantDomain_610509DCF51E0FE136D0A5F0519FCE00_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_alx_RealEstatePropertyOccupantAxis_7D97CA18DC11B66AA71AA5F0519F48CB" xlink:to="loc_alx_RealEstatePropertyOccupantDomain_610509DCF51E0FE136D0A5F0519FCE00_default" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RealEstatePropertyOccupantDomain" xlink:label="loc_alx_RealEstatePropertyOccupantDomain_610509DCF51E0FE136D0A5F0519FCE00" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_alx_RealEstatePropertyOccupantAxis_7D97CA18DC11B66AA71AA5F0519F48CB" xlink:to="loc_alx_RealEstatePropertyOccupantDomain_610509DCF51E0FE136D0A5F0519FCE00" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_IkeaMember" xlink:label="loc_alx_IkeaMember_010DE0B3571219438C2FA5F0519F368C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_RealEstatePropertyOccupantDomain_610509DCF51E0FE136D0A5F0519FCE00" xlink:to="loc_alx_IkeaMember_010DE0B3571219438C2FA5F0519F368C" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RegoPark1PropertyMember" xlink:label="loc_alx_RegoPark1PropertyMember_5C90923224116EC5F3CFA5F0519F95BE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_RealEstatePropertyOccupantDomain_610509DCF51E0FE136D0A5F0519FCE00" xlink:to="loc_alx_RegoPark1PropertyMember_5C90923224116EC5F3CFA5F0519F95BE" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_SearsMember" xlink:label="loc_alx_SearsMember_A6CE32EFE4E07F529799A5F0519FA96E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_RealEstatePropertyOccupantDomain_610509DCF51E0FE136D0A5F0519FCE00" xlink:to="loc_alx_SearsMember_A6CE32EFE4E07F529799A5F0519FA96E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:label="loc_srt_RangeAxis_0429CD02A58A63A97386A5F051A0748C" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:to="loc_srt_RangeAxis_0429CD02A58A63A97386A5F051A0748C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="loc_srt_RangeMember_B97C778160F4765F27FDA5F051A0DD7E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_0429CD02A58A63A97386A5F051A0748C" xlink:to="loc_srt_RangeMember_B97C778160F4765F27FDA5F051A0DD7E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="loc_srt_RangeMember_B97C778160F4765F27FDA5F051A0DD7E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_0429CD02A58A63A97386A5F051A0748C" xlink:to="loc_srt_RangeMember_B97C778160F4765F27FDA5F051A0DD7E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember" xlink:label="loc_srt_MinimumMember_5DE4613FE5DA0E03D8B2A5F051A0B0F3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_B97C778160F4765F27FDA5F051A0DD7E" xlink:to="loc_srt_MinimumMember_5DE4613FE5DA0E03D8B2A5F051A0B0F3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember" xlink:label="loc_srt_MaximumMember_DE01E963E09BF5E02ACAA5F051A150B3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_B97C778160F4765F27FDA5F051A0DD7E" xlink:to="loc_srt_MaximumMember_DE01E963E09BF5E02ACAA5F051A150B3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_1DA27E120CDAE3ED4CA6A5F051A1CD95" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_0509F28F7DCD9B1B97E0A5F0519891E4" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_1DA27E120CDAE3ED4CA6A5F051A1CD95" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="loc_us-gaap_LossContingencyNatureDomain_ED86229FD525A66D8CF4A5F051A1BDB2_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_1DA27E120CDAE3ED4CA6A5F051A1CD95" xlink:to="loc_us-gaap_LossContingencyNatureDomain_ED86229FD525A66D8CF4A5F051A1BDB2_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="loc_us-gaap_LossContingencyNatureDomain_ED86229FD525A66D8CF4A5F051A1BDB2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_1DA27E120CDAE3ED4CA6A5F051A1CD95" xlink:to="loc_us-gaap_LossContingencyNatureDomain_ED86229FD525A66D8CF4A5F051A1BDB2" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_EstimatedFutureDamagesMember" xlink:label="loc_alx_EstimatedFutureDamagesMember_ECB4C267F28715762D3DA5F051A12B61" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_ED86229FD525A66D8CF4A5F051A1BDB2" xlink:to="loc_alx_EstimatedFutureDamagesMember_ECB4C267F28715762D3DA5F051A12B61" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_InsuranceMaximumCoveragePerIncident" xlink:label="loc_alx_InsuranceMaximumCoveragePerIncident_BED39088B8E7732DC28FA5F051A27CE0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_InsuranceMaximumCoveragePerIncident_BED39088B8E7732DC28FA5F051A27CE0" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_InsuranceMaximumCoveragePerProperty" xlink:label="loc_alx_InsuranceMaximumCoveragePerProperty_B19C0D3F43B5CD2F7271A5F051A2D796" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_InsuranceMaximumCoveragePerProperty_B19C0D3F43B5CD2F7271A5F051A2D796" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_InsuranceMaximumCoverageInAggregate" xlink:label="loc_alx_InsuranceMaximumCoverageInAggregate_F3C240F230311899967CA5F051A205E4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_InsuranceMaximumCoverageInAggregate_F3C240F230311899967CA5F051A205E4" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_InsuranceCoverageEndDate" xlink:label="loc_alx_InsuranceCoverageEndDate_25791C2A028EFCF4E8C7A5F051A25F4E" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_InsuranceCoverageEndDate_25791C2A028EFCF4E8C7A5F051A25F4E" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_InsuranceDeductible" xlink:label="loc_alx_InsuranceDeductible_01BEDC6F4A59CFC60F2FA5F051A37023" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_InsuranceDeductible_01BEDC6F4A59CFC60F2FA5F051A37023" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_SelfInsuredResponsibility" xlink:label="loc_alx_SelfInsuredResponsibility_1E4D51C1948AA37A0A3EA5F051A3E4C6" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_SelfInsuredResponsibility_1E4D51C1948AA37A0A3EA5F051A3E4C6" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_FederalGovernmentResponsibility" xlink:label="loc_alx_FederalGovernmentResponsibility_D33B5F7F945F4BB727C6A5F051A35D29" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_FederalGovernmentResponsibility_D33B5F7F945F4BB727C6A5F051A35D29" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AreaOfLand" xlink:label="loc_us-gaap_AreaOfLand_20A2BAB6D954637BDD16A5F051A35ED0" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_AreaOfLand_20A2BAB6D954637BDD16A5F051A35ED0" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PropertyPurchaseOptionExercisableByLessee" xlink:label="loc_alx_PropertyPurchaseOptionExercisableByLessee_86CCE325017FAA53DA6FA5F051A376C6" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_PropertyPurchaseOptionExercisableByLessee_86CCE325017FAA53DA6FA5F051A376C6" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PurchaseOptionNotExercisedAmountIncludedInTripleNetRentOverRemainderOfLease" xlink:label="loc_alx_PurchaseOptionNotExercisedAmountIncludedInTripleNetRentOverRemainderOfLease_1A73B17BEEF7F5BF8C81A5F051A4D097" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_PurchaseOptionNotExercisedAmountIncludedInTripleNetRentOverRemainderOfLease_1A73B17BEEF7F5BF8C81A5F051A4D097" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_AFAA1BED6049CD06DA9AA5F051A46725" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_AFAA1BED6049CD06DA9AA5F051A46725" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_TripleNetRentAnnualAmount" xlink:label="loc_alx_TripleNetRentAnnualAmount_273BBFD3C2509C2593ACA5F051A4FFE5" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_TripleNetRentAnnualAmount_273BBFD3C2509C2593ACA5F051A4FFE5" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PurchaseOptionExercisedProceedsFromSaleOfLandHeldForUse" xlink:label="loc_alx_PurchaseOptionExercisedProceedsFromSaleOfLandHeldForUse_C64E3080CAA18FD5D60FA5F051A4C786" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_PurchaseOptionExercisedProceedsFromSaleOfLandHeldForUse_C64E3080CAA18FD5D60FA5F051A4C786" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GainLossOnDispositionOfRealEstateDiscontinuedOperations" xlink:label="loc_us-gaap_GainLossOnDispositionOfRealEstateDiscontinuedOperations_A4656EF1D16E91C61EAAA5F051A46042" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_GainLossOnDispositionOfRealEstateDiscontinuedOperations_A4656EF1D16E91C61EAAA5F051A46042" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_LeasesOfLessorRentalTermRange" xlink:label="loc_alx_LeasesOfLessorRentalTermRange_07A868A1778E74A3A59FA5F051A4ECE5" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_LeasesOfLessorRentalTermRange_07A868A1778E74A3A59FA5F051A4ECE5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesPayable" xlink:label="loc_us-gaap_NotesPayable_7639A965AC16967919CFA5F051A5A7DE" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_NotesPayable_7639A965AC16967919CFA5F051A5A7DE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:label="loc_us-gaap_DebtInstrumentMaturityDate_59228E25AF9AE939C93BA5F051A5C8B8" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_DebtInstrumentMaturityDate_59228E25AF9AE939C93BA5F051A5C8B8" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_LoanAmortizationPeriod" xlink:label="loc_alx_LoanAmortizationPeriod_5175587BE3C5D94B637EA5F051A5FAA7" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_LoanAmortizationPeriod_5175587BE3C5D94B637EA5F051A5FAA7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AreaOfRealEstateProperty" xlink:label="loc_us-gaap_AreaOfRealEstateProperty_9B8FCF40E36022162D7AA5F051A623D5" xlink:type="locator" />
    <link:definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_AreaOfRealEstateProperty_9B8FCF40E36022162D7AA5F051A623D5" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_NumberOfFires" xlink:label="loc_alx_NumberOfFires_4F3210FD6C1A879D0EE1A5F051A6E043" xlink:type="locator" />
    <link:definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_NumberOfFires_4F3210FD6C1A879D0EE1A5F051A6E043" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingencyDamagesSoughtValue" xlink:label="loc_us-gaap_LossContingencyDamagesSoughtValue_0A2F1509B05AB056960CA5F051A6092A" xlink:type="locator" />
    <link:definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_LossContingencyDamagesSoughtValue_0A2F1509B05AB056960CA5F051A6092A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_02B6788C1BA5FC2D49C4A5F051A67770" xlink:type="locator" />
    <link:definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_02B6788C1BA5FC2D49C4A5F051A67770" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RealEstateTaxExpense" xlink:label="loc_us-gaap_RealEstateTaxExpense_533FE77FBF619CD23CE3A5F051A7BF90" xlink:type="locator" />
    <link:definitionArc order="23" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_RealEstateTaxExpense_533FE77FBF619CD23CE3A5F051A7BF90" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_AdditionalRealEstateTransferTax" xlink:label="loc_alx_AdditionalRealEstateTransferTax_BEB739CD5EB4BA13FA9DA5F051A72EEE" xlink:type="locator" />
    <link:definitionArc order="24" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_AdditionalRealEstateTransferTax_BEB739CD5EB4BA13FA9DA5F051A72EEE" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RealEstateTaxExpenseInterest" xlink:label="loc_alx_RealEstateTaxExpenseInterest_1B321DA44C1B9B8B5E35A5F051A70B8B" xlink:type="locator" />
    <link:definitionArc order="25" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_alx_RealEstateTaxExpenseInterest_1B321DA44C1B9B8B5E35A5F051A70B8B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_1B637FAE30DEFF6A7BCAA5F051A7AB2D" xlink:type="locator" />
    <link:definitionArc order="26" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_3A53A5EABAA33FE2E361A5F051A21B3F" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_1B637FAE30DEFF6A7BCAA5F051A7AB2D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedBalanceSheetsUnaudited" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedBalanceSheetsUnauditedParenthetical" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsOfCashFlowsUnauditedParenthetical" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_A909D5F946324C530FF9E10FBC405E4E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_702DA548622E72E10E1FE10FBC3EE6E5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_A909D5F946324C530FF9E10FBC405E4E" xlink:to="loc_us-gaap_StatementTable_702DA548622E72E10E1FE10FBC3EE6E5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_F92B4EA33444585703AAE10FBC3ECBDC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_702DA548622E72E10E1FE10FBC3EE6E5" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_F92B4EA33444585703AAE10FBC3ECBDC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_016CAF1F22D091C7F340E10FBC3F923A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_F92B4EA33444585703AAE10FBC3ECBDC" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_016CAF1F22D091C7F340E10FBC3F923A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_016CAF1F22D091C7F340E10FBC3F923A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_F92B4EA33444585703AAE10FBC3ECBDC" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_016CAF1F22D091C7F340E10FBC3F923A" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_DevelopmentFeesMember" xlink:label="loc_alx_DevelopmentFeesMember_FDA1F5C6F3E9F5BD5341E10FBC3F31C5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_016CAF1F22D091C7F340E10FBC3F923A" xlink:to="loc_alx_DevelopmentFeesMember_FDA1F5C6F3E9F5BD5341E10FBC3F31C5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_1774EAF71AFE669DAC81E10FBC3F80B3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_702DA548622E72E10E1FE10FBC3EE6E5" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_1774EAF71AFE669DAC81E10FBC3F80B3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_0CE167500536227C7550E10FBC4011FF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_1774EAF71AFE669DAC81E10FBC3F80B3" xlink:to="loc_us-gaap_RelatedPartyDomain_0CE167500536227C7550E10FBC4011FF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_0CE167500536227C7550E10FBC4011FF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_1774EAF71AFE669DAC81E10FBC3F80B3" xlink:to="loc_us-gaap_RelatedPartyDomain_0CE167500536227C7550E10FBC4011FF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_AffiliatedEntityMember" xlink:label="loc_srt_AffiliatedEntityMember_56E7EBBC7AE8F406E23FE10FBC401160" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_0CE167500536227C7550E10FBC4011FF" xlink:to="loc_srt_AffiliatedEntityMember_56E7EBBC7AE8F406E23FE10FBC401160" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_NonCashAdditionsToRealEstate" xlink:label="loc_alx_NonCashAdditionsToRealEstate_6582F946AAF5BEAB83A6E10FBC40BEE5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_A909D5F946324C530FF9E10FBC405E4E" xlink:to="loc_alx_NonCashAdditionsToRealEstate_6582F946AAF5BEAB83A6E10FBC40BEE5" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsOfChangesInEquityUnaudited" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_99A6AB1A8132BDFD4CC57841AEE6C2B0" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_89CED0F29A2C557A25957841AEE4B63A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_99A6AB1A8132BDFD4CC57841AEE6C2B0" xlink:to="loc_us-gaap_StatementTable_89CED0F29A2C557A25957841AEE4B63A" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_BED9E3F5F532318D08657841AEE5D7D4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_89CED0F29A2C557A25957841AEE4B63A" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_BED9E3F5F532318D08657841AEE5D7D4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_30C67087DB3275A412DB7841AEE557A9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_BED9E3F5F532318D08657841AEE5D7D4" xlink:to="loc_us-gaap_EquityComponentDomain_30C67087DB3275A412DB7841AEE557A9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_30C67087DB3275A412DB7841AEE557A9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_BED9E3F5F532318D08657841AEE5D7D4" xlink:to="loc_us-gaap_EquityComponentDomain_30C67087DB3275A412DB7841AEE557A9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_09A6389BF0C6783843857841AEE50532" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_30C67087DB3275A412DB7841AEE557A9" xlink:to="loc_us-gaap_CommonStockMember_09A6389BF0C6783843857841AEE50532" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_09F89B452D6F412D96F27841AEE6F39F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_30C67087DB3275A412DB7841AEE557A9" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_09F89B452D6F412D96F27841AEE6F39F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_82FE5F959C02677783F57841AEE65E3A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_30C67087DB3275A412DB7841AEE557A9" xlink:to="loc_us-gaap_RetainedEarningsMember_82FE5F959C02677783F57841AEE65E3A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_F7CB1371C08FFCC337227841AEE64E1B" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_30C67087DB3275A412DB7841AEE557A9" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_F7CB1371C08FFCC337227841AEE64E1B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TreasuryStockMember" xlink:label="loc_us-gaap_TreasuryStockMember_6C5F5D88D266EB95A6C07841AEE6B615" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_30C67087DB3275A412DB7841AEE557A9" xlink:to="loc_us-gaap_TreasuryStockMember_6C5F5D88D266EB95A6C07841AEE6B615" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1CE5378BFC814A3D61F57841AEE6EC15" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99A6AB1A8132BDFD4CC57841AEE6C2B0" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1CE5378BFC814A3D61F57841AEE6EC15" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaap_CommonStockSharesIssued_EA2DB26D465D6BF404567841AEE74070" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1CE5378BFC814A3D61F57841AEE6EC15" xlink:to="loc_us-gaap_CommonStockSharesIssued_EA2DB26D465D6BF404567841AEE74070" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_43F76F96A52D5BFECB7B7841AEE7B1CE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1CE5378BFC814A3D61F57841AEE6EC15" xlink:to="loc_us-gaap_StockholdersEquity_43F76F96A52D5BFECB7B7841AEE7B1CE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_E7B6CB7D50E585C250C67841AEE712AC" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1CE5378BFC814A3D61F57841AEE6EC15" xlink:to="loc_us-gaap_NetIncomeLoss_E7B6CB7D50E585C250C67841AEE712AC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DividendsCommonStockCash" xlink:label="loc_us-gaap_DividendsCommonStockCash_48FCBB41D133E5EB32BA7841AEE871DF" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1CE5378BFC814A3D61F57841AEE6EC15" xlink:to="loc_us-gaap_DividendsCommonStockCash_48FCBB41D133E5EB32BA7841AEE871DF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_DA92139FFB5143219D327841AEE82EA1" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1CE5378BFC814A3D61F57841AEE6EC15" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_DA92139FFB5143219D327841AEE82EA1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation" xlink:label="loc_us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation_398CEB19DA0F478DB14A7841AEE8F49C" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1CE5378BFC814A3D61F57841AEE6EC15" xlink:to="loc_us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation_398CEB19DA0F478DB14A7841AEE8F49C" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsOfChangesInEquityUnauditedParenthetical" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsOfComprehensiveIncomeUnaudited" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsOfIncomeUnaudited" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsOfIncomeUnauditedParenthetical" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/Covid19Pandemic" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/Covid19PandemicNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnusualOrInfrequentItemLineItems" xlink:label="loc_us-gaap_UnusualOrInfrequentItemLineItems_732F2F8D0F2600D98481A0ED8531E6AB" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnusualOrInfrequentItemTable" xlink:label="loc_us-gaap_UnusualOrInfrequentItemTable_C8B60F2D449E3C95AD07A0ED85287F0D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_UnusualOrInfrequentItemLineItems_732F2F8D0F2600D98481A0ED8531E6AB" xlink:to="loc_us-gaap_UnusualOrInfrequentItemTable_C8B60F2D449E3C95AD07A0ED85287F0D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_0C76C12CE5E6363D0861A0ED8529B15E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_UnusualOrInfrequentItemTable_C8B60F2D449E3C95AD07A0ED85287F0D" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_0C76C12CE5E6363D0861A0ED8529B15E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_15B9271EEE6F9987F6C4A0ED8529CB85_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_0C76C12CE5E6363D0861A0ED8529B15E" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_15B9271EEE6F9987F6C4A0ED8529CB85_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_15B9271EEE6F9987F6C4A0ED8529CB85" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_0C76C12CE5E6363D0861A0ED8529B15E" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_15B9271EEE6F9987F6C4A0ED8529CB85" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_OfficeBuildingMember" xlink:label="loc_srt_OfficeBuildingMember_2F67BA475B9466706B6BA0EF4A769FE9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_15B9271EEE6F9987F6C4A0ED8529CB85" xlink:to="loc_srt_OfficeBuildingMember_2F67BA475B9466706B6BA0EF4A769FE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RetailSiteMember" xlink:label="loc_srt_RetailSiteMember_079AFEFE916CE77EDEDCA0ED852A00B2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_15B9271EEE6F9987F6C4A0ED8529CB85" xlink:to="loc_srt_RetailSiteMember_079AFEFE916CE77EDEDCA0ED852A00B2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResidentialRealEstateMember" xlink:label="loc_us-gaap_ResidentialRealEstateMember_24B9C291C4B57A85512FA0ED852AA45D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_15B9271EEE6F9987F6C4A0ED8529CB85" xlink:to="loc_us-gaap_ResidentialRealEstateMember_24B9C291C4B57A85512FA0ED852AA45D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_AD30B476B8795B6BBDF1A0ED852A982B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_UnusualOrInfrequentItemTable_C8B60F2D449E3C95AD07A0ED85287F0D" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_AD30B476B8795B6BBDF1A0ED852A982B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_6D3E818559A070810C54A0ED852AB985_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_AD30B476B8795B6BBDF1A0ED852A982B" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_6D3E818559A070810C54A0ED852AB985_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_6D3E818559A070810C54A0ED852AB985" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_AD30B476B8795B6BBDF1A0ED852A982B" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_6D3E818559A070810C54A0ED852AB985" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_SevenThreeOneLexingtonAvenuePropertyMember" xlink:label="loc_alx_SevenThreeOneLexingtonAvenuePropertyMember_E2D858052470C2516CF4A0ED8530FBE6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_6D3E818559A070810C54A0ED852AB985" xlink:to="loc_alx_SevenThreeOneLexingtonAvenuePropertyMember_E2D858052470C2516CF4A0ED8530FBE6" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_AlexanderApartmentTowerMember" xlink:label="loc_alx_AlexanderApartmentTowerMember_275597EF8E0B6C03100CA0ED8530E205" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_6D3E818559A070810C54A0ED852AB985" xlink:to="loc_alx_AlexanderApartmentTowerMember_275597EF8E0B6C03100CA0ED8530E205" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnusualOrInfrequentItemAxis" xlink:label="loc_us-gaap_UnusualOrInfrequentItemAxis_F59885040DB091D160A3A0ED853071F0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_UnusualOrInfrequentItemTable_C8B60F2D449E3C95AD07A0ED85287F0D" xlink:to="loc_us-gaap_UnusualOrInfrequentItemAxis_F59885040DB091D160A3A0ED853071F0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnusualOrInfrequentItemDomain" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_90286B7327CE775721C1A0ED85317A04_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_UnusualOrInfrequentItemAxis_F59885040DB091D160A3A0ED853071F0" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_90286B7327CE775721C1A0ED85317A04_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnusualOrInfrequentItemDomain" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_90286B7327CE775721C1A0ED85317A04" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_UnusualOrInfrequentItemAxis_F59885040DB091D160A3A0ED853071F0" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_90286B7327CE775721C1A0ED85317A04" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_COVID19Member" xlink:label="loc_alx_COVID19Member_5C0F55FC38E5680C18FAA0ED8531DFE0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemDomain_90286B7327CE775721C1A0ED85317A04" xlink:to="loc_alx_COVID19Member_5C0F55FC38E5680C18FAA0ED8531DFE0" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RentCollectedPercent" xlink:label="loc_alx_RentCollectedPercent_CAF95CCCE15E89A614A8A0ED85314543" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemLineItems_732F2F8D0F2600D98481A0ED8531E6AB" xlink:to="loc_alx_RentCollectedPercent_CAF95CCCE15E89A614A8A0ED85314543" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RentCollectedDeferredPercent" xlink:label="loc_alx_RentCollectedDeferredPercent_3FD52D7CC94B5E1862DCA0ED8532B474" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemLineItems_732F2F8D0F2600D98481A0ED8531E6AB" xlink:to="loc_alx_RentCollectedDeferredPercent_3FD52D7CC94B5E1862DCA0ED8532B474" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_A2A6195D218F11AF1533A0ED8532A9D2" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemLineItems_732F2F8D0F2600D98481A0ED8531E6AB" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_A2A6195D218F11AF1533A0ED8532A9D2" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_WriteoffofRentReceivable" xlink:label="loc_alx_WriteoffofRentReceivable_3B319EF452B9E96CD083A0ED8532A579" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemLineItems_732F2F8D0F2600D98481A0ED8531E6AB" xlink:to="loc_alx_WriteoffofRentReceivable_3B319EF452B9E96CD083A0ED8532A579" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/DocumentAndEntityInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/EarningsPerShare" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/EarningsPerShareNarrativeDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/EarningsPerShareScheduleOfEarningsPerShareBasicAndDilutedDetail" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/EarningsPerShareTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/FairValueMeasurements" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/FairValueMeasurementsFinancialAssetsAndLiabilitiesMeasuredAtFairValueDetail" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7B0FAB50EA4F5A6F6CE4E10FBA8DD6C5" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7C708EB2F93279A9E2A9E10FBA8AB4FB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7B0FAB50EA4F5A6F6CE4E10FBA8DD6C5" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7C708EB2F93279A9E2A9E10FBA8AB4FB" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentTypeAxis" xlink:label="loc_us-gaap_InvestmentTypeAxis_D6B1418B951B89DED7FDE10FBA8AC256" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7C708EB2F93279A9E2A9E10FBA8AB4FB" xlink:to="loc_us-gaap_InvestmentTypeAxis_D6B1418B951B89DED7FDE10FBA8AC256" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_5D44EABA96BC16392345E10FBA8A52C9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_D6B1418B951B89DED7FDE10FBA8AC256" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_5D44EABA96BC16392345E10FBA8A52C9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_5D44EABA96BC16392345E10FBA8A52C9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_D6B1418B951B89DED7FDE10FBA8AC256" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_5D44EABA96BC16392345E10FBA8A52C9" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_MarketableSecuritiesMember" xlink:label="loc_alx_MarketableSecuritiesMember_B83FFC55CE8836935299E10FBA8B495D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_5D44EABA96BC16392345E10FBA8A52C9" xlink:to="loc_alx_MarketableSecuritiesMember_B83FFC55CE8836935299E10FBA8B495D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_4E427411A6901CEA7055E10FBA8B2804" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7C708EB2F93279A9E2A9E10FBA8AB4FB" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_4E427411A6901CEA7055E10FBA8B2804" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_7204F7A54A3A3546A1EBE10FBA8BF12F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_4E427411A6901CEA7055E10FBA8B2804" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_7204F7A54A3A3546A1EBE10FBA8BF12F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_7204F7A54A3A3546A1EBE10FBA8BF12F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_4E427411A6901CEA7055E10FBA8B2804" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_7204F7A54A3A3546A1EBE10FBA8BF12F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_D37BC62F418F1E7E31D9E10FBA8C4505" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_7204F7A54A3A3546A1EBE10FBA8BF12F" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_D37BC62F418F1E7E31D9E10FBA8C4505" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_CEC77BAE53942E1D36ECE10FBA8C60BA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7C708EB2F93279A9E2A9E10FBA8AB4FB" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_CEC77BAE53942E1D36ECE10FBA8C60BA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_60077C99548636777295E10FBA8C1245_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_CEC77BAE53942E1D36ECE10FBA8C60BA" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_60077C99548636777295E10FBA8C1245_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_60077C99548636777295E10FBA8C1245" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_CEC77BAE53942E1D36ECE10FBA8C60BA" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_60077C99548636777295E10FBA8C1245" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_79F467C896E9D436F14AE10FBA8C45FE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_60077C99548636777295E10FBA8C1245" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_79F467C896E9D436F14AE10FBA8C45FE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_B160745D0639A74749BCE10FBA8D1BA0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_60077C99548636777295E10FBA8C1245" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_B160745D0639A74749BCE10FBA8D1BA0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_6E0DA0CDADDD92F16D71E10FBA8DC182" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_60077C99548636777295E10FBA8C1245" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_6E0DA0CDADDD92F16D71E10FBA8DC182" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_2562038245896AF0A834E10FBA8D122E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7B0FAB50EA4F5A6F6CE4E10FBA8DD6C5" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_2562038245896AF0A834E10FBA8D122E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/FairValueMeasurementsFinancialAssetsAndLiabilitiesNotMeasuredAtFairValueDetail" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_52045EAD630DB42D4D70E10FBACD42B5" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_8AFDAD329D40371AD550E10FBACA9EE7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_52045EAD630DB42D4D70E10FBACD42B5" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_8AFDAD329D40371AD550E10FBACA9EE7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_CB5B882ED57B82B6897AE10FBACAE043" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_8AFDAD329D40371AD550E10FBACA9EE7" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_CB5B882ED57B82B6897AE10FBACAE043" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_882A79142AD72BD32EECE10FBACBE90A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_CB5B882ED57B82B6897AE10FBACAE043" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_882A79142AD72BD32EECE10FBACBE90A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_71BDCCB276381414E169E10FBACA626C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_CB5B882ED57B82B6897AE10FBACAE043" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_71BDCCB276381414E169E10FBACA626C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_882A79142AD72BD32EECE10FBACBE90A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_71BDCCB276381414E169E10FBACA626C" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_882A79142AD72BD32EECE10FBACBE90A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_FFA89E4CD3EA29987E1BE10FBACC7935" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_71BDCCB276381414E169E10FBACA626C" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_FFA89E4CD3EA29987E1BE10FBACC7935" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_613573551D3133C79796E10FBACC1A51" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_71BDCCB276381414E169E10FBACA626C" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_613573551D3133C79796E10FBACC1A51" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_6EF5FC561827022A580FE10FBACC289C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_8AFDAD329D40371AD550E10FBACA9EE7" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_6EF5FC561827022A580FE10FBACC289C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9F82B6B0A4DE258DD4A4E10FBACCFE9D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_6EF5FC561827022A580FE10FBACC289C" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9F82B6B0A4DE258DD4A4E10FBACCFE9D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9F82B6B0A4DE258DD4A4E10FBACCFE9D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_6EF5FC561827022A580FE10FBACC289C" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9F82B6B0A4DE258DD4A4E10FBACCFE9D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_A1BD4A71F7031E9A520AE10FBACD88DF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9F82B6B0A4DE258DD4A4E10FBACCFE9D" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_A1BD4A71F7031E9A520AE10FBACD88DF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_935DFA3B59C51A75187EE10FBACDABD9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9F82B6B0A4DE258DD4A4E10FBACCFE9D" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_935DFA3B59C51A75187EE10FBACDABD9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_AB2EC48B57737DBE1338E10FBACD0CB5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_52045EAD630DB42D4D70E10FBACD42B5" xlink:to="loc_us-gaap_AssetsAbstract_AB2EC48B57737DBE1338E10FBACD0CB5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_B45BA1A8C08ABC358C69E10FBACE6397" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AB2EC48B57737DBE1338E10FBACD0CB5" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_B45BA1A8C08ABC358C69E10FBACE6397" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesAbstract" xlink:label="loc_us-gaap_LiabilitiesAbstract_26CF8C2CBD2F898FEDFFE10FBACEA0EE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_52045EAD630DB42D4D70E10FBACD42B5" xlink:to="loc_us-gaap_LiabilitiesAbstract_26CF8C2CBD2F898FEDFFE10FBACEA0EE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesPayableFairValueDisclosure" xlink:label="loc_us-gaap_NotesPayableFairValueDisclosure_F56FBCFB940145931835E10FBACEC01B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_26CF8C2CBD2F898FEDFFE10FBACEA0EE" xlink:to="loc_us-gaap_NotesPayableFairValueDisclosure_F56FBCFB940145931835E10FBACEC01B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/FairValueMeasurementsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MarketableSecurities" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MarketableSecuritiesAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentHoldingsLineItems" xlink:label="loc_us-gaap_InvestmentHoldingsLineItems_96B367EDE04217D93C7777EA88E7CA28" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentHoldingsTable" xlink:label="loc_us-gaap_InvestmentHoldingsTable_FBCB7B781FF1075B041577EA88E501B8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InvestmentHoldingsLineItems_96B367EDE04217D93C7777EA88E7CA28" xlink:to="loc_us-gaap_InvestmentHoldingsTable_FBCB7B781FF1075B041577EA88E501B8" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentTypeAxis" xlink:label="loc_us-gaap_InvestmentTypeAxis_3DEE8F83B65D15E6281477EA88E68483" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentHoldingsTable_FBCB7B781FF1075B041577EA88E501B8" xlink:to="loc_us-gaap_InvestmentTypeAxis_3DEE8F83B65D15E6281477EA88E68483" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_C9F098690CE9AFF6FDA077EA88E638A7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_3DEE8F83B65D15E6281477EA88E68483" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_C9F098690CE9AFF6FDA077EA88E638A7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_C9F098690CE9AFF6FDA077EA88E638A7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_3DEE8F83B65D15E6281477EA88E68483" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_C9F098690CE9AFF6FDA077EA88E638A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_CF152A6D4B240079515277EA88E65812" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_C9F098690CE9AFF6FDA077EA88E638A7" xlink:to="loc_us-gaap_CommonStockMember_CF152A6D4B240079515277EA88E65812" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_CED549BB907D5D38EB0377EA88E70E3C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentHoldingsTable_FBCB7B781FF1075B041577EA88E501B8" xlink:to="loc_dei_LegalEntityAxis_CED549BB907D5D38EB0377EA88E70E3C" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_50791F188CD37C66889277EA88E7D1CA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_CED549BB907D5D38EB0377EA88E70E3C" xlink:to="loc_dei_EntityDomain_50791F188CD37C66889277EA88E7D1CA_default" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_50791F188CD37C66889277EA88E7D1CA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_CED549BB907D5D38EB0377EA88E70E3C" xlink:to="loc_dei_EntityDomain_50791F188CD37C66889277EA88E7D1CA" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_MacerichMember" xlink:label="loc_alx_MacerichMember_DFA02205966B8251FD0477EA88E7C2B3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_50791F188CD37C66889277EA88E7D1CA" xlink:to="loc_alx_MacerichMember_DFA02205966B8251FD0477EA88E7C2B3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentOwnedBalanceShares" xlink:label="loc_us-gaap_InvestmentOwnedBalanceShares_B57937A27BCE1BAD162A77EA88E8DC37" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentHoldingsLineItems_96B367EDE04217D93C7777EA88E7CA28" xlink:to="loc_us-gaap_InvestmentOwnedBalanceShares_B57937A27BCE1BAD162A77EA88E8DC37" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MarketableSecurities" xlink:label="loc_us-gaap_MarketableSecurities_BC15083A67FC4F56B78377EA88E87C7E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentHoldingsLineItems_96B367EDE04217D93C7777EA88E7CA28" xlink:to="loc_us-gaap_MarketableSecurities_BC15083A67FC4F56B78377EA88E87C7E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharePrice" xlink:label="loc_us-gaap_SharePrice_B35FACD13F7B060C4A9377EA88E82304" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentHoldingsLineItems_96B367EDE04217D93C7777EA88E7CA28" xlink:to="loc_us-gaap_SharePrice_B35FACD13F7B060C4A9377EA88E82304" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MortgagesPayable" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MortgagesPayableAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateLineItems" xlink:label="loc_srt_MortgageLoansOnRealEstateLineItems_7020D7F259ADB5F98E58A62867102608" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateScheduleTable" xlink:label="loc_srt_MortgageLoansOnRealEstateScheduleTable_E1E3947B8A255416BD0FA628670938EC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_7020D7F259ADB5F98E58A62867102608" xlink:to="loc_srt_MortgageLoansOnRealEstateScheduleTable_E1E3947B8A255416BD0FA628670938EC" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaap_TypeOfArrangementAxis_1F0E90573D7C70537685A628670A24C8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_E1E3947B8A255416BD0FA628670938EC" xlink:to="loc_us-gaap_TypeOfArrangementAxis_1F0E90573D7C70537685A628670A24C8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_854F11D0114612BF4825A628670B69C5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_1F0E90573D7C70537685A628670A24C8" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_854F11D0114612BF4825A628670B69C5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_854F11D0114612BF4825A628670B69C5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_1F0E90573D7C70537685A628670A24C8" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_854F11D0114612BF4825A628670B69C5" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ParticipationAgreementMember" xlink:label="loc_alx_ParticipationAgreementMember_FAF8DD3F1E9CDBA3AE80A628670B9AEC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_854F11D0114612BF4825A628670B69C5" xlink:to="loc_alx_ParticipationAgreementMember_FAF8DD3F1E9CDBA3AE80A628670B9AEC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_1C5D85C35A0A262570D3A628670CBE81" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_E1E3947B8A255416BD0FA628670938EC" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_1C5D85C35A0A262570D3A628670CBE81" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_EFEE1E078D8E3DDCF3E1A628670CA873_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_1C5D85C35A0A262570D3A628670CBE81" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_EFEE1E078D8E3DDCF3E1A628670CA873_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_EFEE1E078D8E3DDCF3E1A628670CA873" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_1C5D85C35A0A262570D3A628670CBE81" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_EFEE1E078D8E3DDCF3E1A628670CA873" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RegoPark2PropertyMember" xlink:label="loc_alx_RegoPark2PropertyMember_3408472399D5B7AA9798A628670CE8B6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_EFEE1E078D8E3DDCF3E1A628670CA873" xlink:to="loc_alx_RegoPark2PropertyMember_3408472399D5B7AA9798A628670CE8B6" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_LexingtonAvenuePropertyMember" xlink:label="loc_alx_LexingtonAvenuePropertyMember_CC6C031CC7B717A96988A628670CAC64" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_EFEE1E078D8E3DDCF3E1A628670CA873" xlink:to="loc_alx_LexingtonAvenuePropertyMember_CC6C031CC7B717A96988A628670CAC64" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_C6F9280E9993A6839711A628670DEB70" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_E1E3947B8A255416BD0FA628670938EC" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_C6F9280E9993A6839711A628670DEB70" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_A3F882DEF908F4255400A628670D676C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_C6F9280E9993A6839711A628670DEB70" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_A3F882DEF908F4255400A628670D676C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_A3F882DEF908F4255400A628670D676C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_C6F9280E9993A6839711A628670DEB70" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_A3F882DEF908F4255400A628670D676C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RetailSiteMember" xlink:label="loc_srt_RetailSiteMember_1A7A49D64699103FFBE0A628670D0BD0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_A3F882DEF908F4255400A628670D676C" xlink:to="loc_srt_RetailSiteMember_1A7A49D64699103FFBE0A628670D0BD0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_OfficeBuildingMember" xlink:label="loc_srt_OfficeBuildingMember_B0A9A58061888B189F58A628670E4374" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_A3F882DEF908F4255400A628670D676C" xlink:to="loc_srt_OfficeBuildingMember_B0A9A58061888B189F58A628670E4374" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_0AA801D776D4E2DA9143A628670E908A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_E1E3947B8A255416BD0FA628670938EC" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_0AA801D776D4E2DA9143A628670E908A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_3433E283A5EF9477F0A3A628670E5B5D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_0AA801D776D4E2DA9143A628670E908A" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_3433E283A5EF9477F0A3A628670E5B5D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_3433E283A5EF9477F0A3A628670E5B5D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_0AA801D776D4E2DA9143A628670E908A" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_3433E283A5EF9477F0A3A628670E5B5D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MortgagesMember" xlink:label="loc_us-gaap_MortgagesMember_0CF0A64E3DDFEF18E7A7A628670E9444" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_3433E283A5EF9477F0A3A628670E5B5D" xlink:to="loc_us-gaap_MortgagesMember_0CF0A64E3DDFEF18E7A7A628670E9444" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VariableRateAxis" xlink:label="loc_us-gaap_VariableRateAxis_95D674461E61636DF79BA628670EF5DE" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_E1E3947B8A255416BD0FA628670938EC" xlink:to="loc_us-gaap_VariableRateAxis_95D674461E61636DF79BA628670EF5DE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_CC4FE48D6004B2684111A628670F7F16_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_95D674461E61636DF79BA628670EF5DE" xlink:to="loc_us-gaap_VariableRateDomain_CC4FE48D6004B2684111A628670F7F16_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_CC4FE48D6004B2684111A628670F7F16" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_95D674461E61636DF79BA628670EF5DE" xlink:to="loc_us-gaap_VariableRateDomain_CC4FE48D6004B2684111A628670F7F16" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_AB4E66E4C230BAF4EFF0A628670F3AD8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_CC4FE48D6004B2684111A628670F7F16" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_AB4E66E4C230BAF4EFF0A628670F3AD8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesPayable" xlink:label="loc_us-gaap_NotesPayable_1E07A0CAA6041CBB6666A62867101F9A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_7020D7F259ADB5F98E58A62867102608" xlink:to="loc_us-gaap_NotesPayable_1E07A0CAA6041CBB6666A62867101F9A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_3876D3865898C7A1EFBDA6286710A958" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_7020D7F259ADB5F98E58A62867102608" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_3876D3865898C7A1EFBDA6286710A958" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_B55674CF7EBFCCEF7BBAA62867108ED0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_7020D7F259ADB5F98E58A62867102608" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_B55674CF7EBFCCEF7BBAA62867108ED0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:label="loc_us-gaap_DebtInstrumentMaturityDate_A210162D0900040E2A82A62867103953" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_7020D7F259ADB5F98E58A62867102608" xlink:to="loc_us-gaap_DebtInstrumentMaturityDate_A210162D0900040E2A82A62867103953" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ParticipatingMortgageLoansParticipationLiabilitiesAmount" xlink:label="loc_us-gaap_ParticipatingMortgageLoansParticipationLiabilitiesAmount_AF0E07571C827E782F30A62867101C62" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_7020D7F259ADB5F98E58A62867102608" xlink:to="loc_us-gaap_ParticipatingMortgageLoansParticipationLiabilitiesAmount_AF0E07571C827E782F30A62867101C62" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromNotesPayable" xlink:label="loc_us-gaap_ProceedsFromNotesPayable_5F49CB90E90D2A8221FDA628671028AB" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_7020D7F259ADB5F98E58A62867102608" xlink:to="loc_us-gaap_ProceedsFromNotesPayable_5F49CB90E90D2A8221FDA628671028AB" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_NotesPayableNet" xlink:label="loc_alx_NotesPayableNet_3F8D6F66B3B824B347E9A6286711CAAE" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_7020D7F259ADB5F98E58A62867102608" xlink:to="loc_alx_NotesPayableNet_3F8D6F66B3B824B347E9A6286711CAAE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:label="loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_68B8B373A50D61A460DDA6286711F536" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_7020D7F259ADB5F98E58A62867102608" xlink:to="loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_68B8B373A50D61A460DDA6286711F536" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MortgagesPayableSummaryOfOutstandingMortgagesPayableDetail" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateLineItems" xlink:label="loc_srt_MortgageLoansOnRealEstateLineItems_38234C653E60A448AFA24E724340156B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateScheduleTable" xlink:label="loc_srt_MortgageLoansOnRealEstateScheduleTable_B7CAFFC13510DDAFD0044E72433DCCE8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_38234C653E60A448AFA24E724340156B" xlink:to="loc_srt_MortgageLoansOnRealEstateScheduleTable_B7CAFFC13510DDAFD0044E72433DCCE8" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_7FDA1979766EC76BC3494E72433DB9BC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_B7CAFFC13510DDAFD0044E72433DCCE8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_7FDA1979766EC76BC3494E72433DB9BC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_282F56EF7B9488C390514E72433DD03D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_7FDA1979766EC76BC3494E72433DB9BC" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_282F56EF7B9488C390514E72433DD03D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_282F56EF7B9488C390514E72433DD03D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_7FDA1979766EC76BC3494E72433DB9BC" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_282F56EF7B9488C390514E72433DD03D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MortgagesMember" xlink:label="loc_us-gaap_MortgagesMember_FC837744E4C839ECEE404E72433E14EC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_282F56EF7B9488C390514E72433DD03D" xlink:to="loc_us-gaap_MortgagesMember_FC837744E4C839ECEE404E72433E14EC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_3F2C99C7AE0BE7C601D74E72433EF129" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_B7CAFFC13510DDAFD0044E72433DCCE8" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_3F2C99C7AE0BE7C601D74E72433EF129" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_D45BB60ED0640733A7B34E72433FC78D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_3F2C99C7AE0BE7C601D74E72433EF129" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_D45BB60ED0640733A7B34E72433FC78D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_D45BB60ED0640733A7B34E72433FC78D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_3F2C99C7AE0BE7C601D74E72433EF129" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_D45BB60ED0640733A7B34E72433FC78D" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_LexingtonAvenuePropertyMember" xlink:label="loc_alx_LexingtonAvenuePropertyMember_42206684CB4DA7AD57444E72433FAE5F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_D45BB60ED0640733A7B34E72433FC78D" xlink:to="loc_alx_LexingtonAvenuePropertyMember_42206684CB4DA7AD57444E72433FAE5F" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ParamusPropertyMember" xlink:label="loc_alx_ParamusPropertyMember_7B53918C22DFE51E2FD14E72433F6BA6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_D45BB60ED0640733A7B34E72433FC78D" xlink:to="loc_alx_ParamusPropertyMember_7B53918C22DFE51E2FD14E72433F6BA6" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RegoPark2PropertyMember" xlink:label="loc_alx_RegoPark2PropertyMember_8E5DCBD39F0B859530DB4E72433F716F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_D45BB60ED0640733A7B34E72433FC78D" xlink:to="loc_alx_RegoPark2PropertyMember_8E5DCBD39F0B859530DB4E72433F716F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_88D04E6C6F685A174D164E7243407E28" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_B7CAFFC13510DDAFD0044E72433DCCE8" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_88D04E6C6F685A174D164E7243407E28" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_C12498516C08679CD2FE4E72434087E3_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_88D04E6C6F685A174D164E7243407E28" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_C12498516C08679CD2FE4E72434087E3_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_C12498516C08679CD2FE4E72434087E3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_88D04E6C6F685A174D164E7243407E28" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_C12498516C08679CD2FE4E72434087E3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RetailSiteMember" xlink:label="loc_srt_RetailSiteMember_7B136F7BC0DF8B37532B4E724340608B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_C12498516C08679CD2FE4E72434087E3" xlink:to="loc_srt_RetailSiteMember_7B136F7BC0DF8B37532B4E724340608B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_OfficeBuildingMember" xlink:label="loc_srt_OfficeBuildingMember_274CB550C6CF0FE9EE254E7243404BAE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_C12498516C08679CD2FE4E72434087E3" xlink:to="loc_srt_OfficeBuildingMember_274CB550C6CF0FE9EE254E7243404BAE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:label="loc_us-gaap_DebtInstrumentMaturityDate_F886A9B0D12E2E66EF3B4E7243413811" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_38234C653E60A448AFA24E724340156B" xlink:to="loc_us-gaap_DebtInstrumentMaturityDate_F886A9B0D12E2E66EF3B4E7243413811" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_A26D67F51A0EC7C4608E4E72434130B4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_38234C653E60A448AFA24E724340156B" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_A26D67F51A0EC7C4608E4E72434130B4" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_NotesPayableGross" xlink:label="loc_alx_NotesPayableGross_E3D2D94DE2DD9757B6BB4E724341FDF6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_38234C653E60A448AFA24E724340156B" xlink:to="loc_alx_NotesPayableGross_E3D2D94DE2DD9757B6BB4E724341FDF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredFinanceCostsNet" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_B8F0B62DFD553C444DD14E7243417E38" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_38234C653E60A448AFA24E724340156B" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_B8F0B62DFD553C444DD14E7243417E38" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesPayable" xlink:label="loc_us-gaap_NotesPayable_4B758C90E177083A0A7E4E724341D51D" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_38234C653E60A448AFA24E724340156B" xlink:to="loc_us-gaap_NotesPayable_4B758C90E177083A0A7E4E724341D51D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedAmortizationDeferredFinanceCosts" xlink:label="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_D71E894A52C5592DEC594E7243425DBA" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_38234C653E60A448AFA24E724340156B" xlink:to="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_D71E894A52C5592DEC594E7243425DBA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MortgagesPayableTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/Organization" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/OrganizationAdditionalInformationDetail" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RecentlyIssuedAccountingLiterature" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RelatedPartyTransactions" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RelatedPartyTransactionsAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F6F1BA8AB8E3613F1BC2E10FBB41CB55" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F6F1BA8AB8E3613F1BC2E10FBB41CB55" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_1C6A3420011276C66E6EE10FBB4188A3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F6F1BA8AB8E3613F1BC2E10FBB41CB55" xlink:to="loc_dei_LegalEntityAxis_1C6A3420011276C66E6EE10FBB4188A3" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_2E604BE52552172CE980E10FBB410F0D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1C6A3420011276C66E6EE10FBB4188A3" xlink:to="loc_dei_EntityDomain_2E604BE52552172CE980E10FBB410F0D_default" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_2E604BE52552172CE980E10FBB410F0D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1C6A3420011276C66E6EE10FBB4188A3" xlink:to="loc_dei_EntityDomain_2E604BE52552172CE980E10FBB410F0D" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_VornadoMember" xlink:label="loc_alx_VornadoMember_596E77094FEC3D6066DAE10FBB4215C0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2E604BE52552172CE980E10FBB410F0D" xlink:to="loc_alx_VornadoMember_596E77094FEC3D6066DAE10FBB4215C0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_OwnershipAxis" xlink:label="loc_srt_OwnershipAxis_C6429A808C3CB7AE1E2AE10FBB420D5D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F6F1BA8AB8E3613F1BC2E10FBB41CB55" xlink:to="loc_srt_OwnershipAxis_C6429A808C3CB7AE1E2AE10FBB420D5D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_OwnershipDomain" xlink:label="loc_srt_OwnershipDomain_F27114754FEA0AA37954E10FBB42024C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_C6429A808C3CB7AE1E2AE10FBB420D5D" xlink:to="loc_srt_OwnershipDomain_F27114754FEA0AA37954E10FBB42024C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_OwnershipDomain" xlink:label="loc_srt_OwnershipDomain_F27114754FEA0AA37954E10FBB42024C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_C6429A808C3CB7AE1E2AE10FBB420D5D" xlink:to="loc_srt_OwnershipDomain_F27114754FEA0AA37954E10FBB42024C" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_AlexandersInc.Member" xlink:label="loc_alx_AlexandersInc.Member_9595A25FDC9A7D76765CE10FBB437D56" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_F27114754FEA0AA37954E10FBB42024C" xlink:to="loc_alx_AlexandersInc.Member_9595A25FDC9A7D76765CE10FBB437D56" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_49DFF3C8FDFC8982BD8FE10FBB43B54B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F6F1BA8AB8E3613F1BC2E10FBB41CB55" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_49DFF3C8FDFC8982BD8FE10FBB43B54B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_5F4B526CD746AC508FF7E10FBB435D9F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_49DFF3C8FDFC8982BD8FE10FBB43B54B" xlink:to="loc_us-gaap_RelatedPartyDomain_5F4B526CD746AC508FF7E10FBB435D9F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_5F4B526CD746AC508FF7E10FBB435D9F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_49DFF3C8FDFC8982BD8FE10FBB43B54B" xlink:to="loc_us-gaap_RelatedPartyDomain_5F4B526CD746AC508FF7E10FBB435D9F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_AffiliatedEntityMember" xlink:label="loc_srt_AffiliatedEntityMember_959970E551A8AA3B0F6DE10FBB43469C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_5F4B526CD746AC508FF7E10FBB435D9F" xlink:to="loc_srt_AffiliatedEntityMember_959970E551A8AA3B0F6DE10FBB43469C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_C80223CF452FD11A39A4E10FBB4324E2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F6F1BA8AB8E3613F1BC2E10FBB41CB55" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_C80223CF452FD11A39A4E10FBB4324E2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_F054D48AAE9D77660A50E10FBB448246_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_C80223CF452FD11A39A4E10FBB4324E2" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_F054D48AAE9D77660A50E10FBB448246_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_F054D48AAE9D77660A50E10FBB448246" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_C80223CF452FD11A39A4E10FBB4324E2" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_F054D48AAE9D77660A50E10FBB448246" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PropertyManagementFeesMember" xlink:label="loc_alx_PropertyManagementFeesMember_B5D954F90C440E2B40E7E10FBB44A87E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_F054D48AAE9D77660A50E10FBB448246" xlink:to="loc_alx_PropertyManagementFeesMember_B5D954F90C440E2B40E7E10FBB44A87E" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_DevelopmentFeesMember" xlink:label="loc_alx_DevelopmentFeesMember_DD2D9977BB8A4C27D5ABE10FBB44446A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_F054D48AAE9D77660A50E10FBB448246" xlink:to="loc_alx_DevelopmentFeesMember_DD2D9977BB8A4C27D5ABE10FBB44446A" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_LeasingFeesMember" xlink:label="loc_alx_LeasingFeesMember_012F11CB51874EEEDE33E10FBB44BB06" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_F054D48AAE9D77660A50E10FBB448246" xlink:to="loc_alx_LeasingFeesMember_012F11CB51874EEEDE33E10FBB44BB06" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ManagementPropertyManagementCleaningEngineeringAndSecurityFeesMember" xlink:label="loc_alx_ManagementPropertyManagementCleaningEngineeringAndSecurityFeesMember_EFEAB7CAC1896645A5AFE10FBB451BB1" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_F054D48AAE9D77660A50E10FBB448246" xlink:to="loc_alx_ManagementPropertyManagementCleaningEngineeringAndSecurityFeesMember_EFEAB7CAC1896645A5AFE10FBB451BB1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_5D806B6C253B3ACB0694E10FBB45C847" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F6F1BA8AB8E3613F1BC2E10FBB41CB55" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_5D806B6C253B3ACB0694E10FBB45C847" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_CE3C17E912C32447BCCAE10FBB45EC99_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_5D806B6C253B3ACB0694E10FBB45C847" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_CE3C17E912C32447BCCAE10FBB45EC99_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_CE3C17E912C32447BCCAE10FBB45EC99" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_5D806B6C253B3ACB0694E10FBB45C847" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_CE3C17E912C32447BCCAE10FBB45EC99" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_RegoPark2PropertyMember" xlink:label="loc_alx_RegoPark2PropertyMember_5E4DA6BC9A58B9DAA9B9E10FBB455C26" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_CE3C17E912C32447BCCAE10FBB45EC99" xlink:to="loc_alx_RegoPark2PropertyMember_5E4DA6BC9A58B9DAA9B9E10FBB455C26" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_LexingtonAvenuePropertyMember" xlink:label="loc_alx_LexingtonAvenuePropertyMember_C3E4BE290F75C4778A45E10FBB4504C1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_CE3C17E912C32447BCCAE10FBB45EC99" xlink:to="loc_alx_LexingtonAvenuePropertyMember_C3E4BE290F75C4778A45E10FBB4504C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_5E799BF7804E61CFB755E10FBB469622" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F6F1BA8AB8E3613F1BC2E10FBB41CB55" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_5E799BF7804E61CFB755E10FBB469622" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_1C62EE6828F0A46597A4E10FBB4601D7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_5E799BF7804E61CFB755E10FBB469622" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_1C62EE6828F0A46597A4E10FBB4601D7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_1C62EE6828F0A46597A4E10FBB4601D7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_5E799BF7804E61CFB755E10FBB469622" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_1C62EE6828F0A46597A4E10FBB4601D7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RetailSiteMember" xlink:label="loc_srt_RetailSiteMember_77CAD432FF19F51357C8E10FBB46CF99" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_1C62EE6828F0A46597A4E10FBB4601D7" xlink:to="loc_srt_RetailSiteMember_77CAD432FF19F51357C8E10FBB46CF99" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_OfficeAndRetailSpaceMember" xlink:label="loc_alx_OfficeAndRetailSpaceMember_0CED7F8CF419F0D8A6C7E10FBB46C71F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_1C62EE6828F0A46597A4E10FBB4601D7" xlink:to="loc_alx_OfficeAndRetailSpaceMember_0CED7F8CF419F0D8A6C7E10FBB46C71F" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_CommonAreaMember" xlink:label="loc_alx_CommonAreaMember_E8C3F49D501552E99641E10FBB47FB52" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_1C62EE6828F0A46597A4E10FBB4601D7" xlink:to="loc_alx_CommonAreaMember_E8C3F49D501552E99641E10FBB47FB52" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_2524BE9CC5EDF59975F8E10FBB476AD6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_2524BE9CC5EDF59975F8E10FBB476AD6" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ManagementFeeAgreementValue" xlink:label="loc_alx_ManagementFeeAgreementValue_87FF9D62BCFABCB9D2DFE10FBB47EFB6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_ManagementFeeAgreementValue_87FF9D62BCFABCB9D2DFE10FBB47EFB6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyManagementFeePercentFee" xlink:label="loc_us-gaap_PropertyManagementFeePercentFee_2AB38D4A732C72B6151BE10FBB478147" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_us-gaap_PropertyManagementFeePercentFee_2AB38D4A732C72B6151BE10FBB478147" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PropertyManagementFeeAgreementPricePerSquareFoot" xlink:label="loc_alx_PropertyManagementFeeAgreementPricePerSquareFoot_7503629E6DE2B1CDCC5AE10FBB47E34C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_PropertyManagementFeeAgreementPricePerSquareFoot_7503629E6DE2B1CDCC5AE10FBB47E34C" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PropertyManagementFeeAgreementValue" xlink:label="loc_alx_PropertyManagementFeeAgreementValue_E371B75AE70BFA9362B5E10FBB487ED2" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_PropertyManagementFeeAgreementValue_E371B75AE70BFA9362B5E10FBB487ED2" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PropertyManagementFeeEscalationPercentagePerAnnum" xlink:label="loc_alx_PropertyManagementFeeEscalationPercentagePerAnnum_499B37D1491FEE7824FBE10FBB48F1EC" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_PropertyManagementFeeEscalationPercentagePerAnnum_499B37D1491FEE7824FBE10FBB48F1EC" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_DevelopmentFeePercentage" xlink:label="loc_alx_DevelopmentFeePercentage_96C5BAFB5B05A12E267AE10FBB48451B" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_DevelopmentFeePercentage_96C5BAFB5B05A12E267AE10FBB48451B" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_LeaseFeePercentageOfRentOneToTenYears" xlink:label="loc_alx_LeaseFeePercentageOfRentOneToTenYears_0C51C62E1126EA282955E10FBB486E6B" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_LeaseFeePercentageOfRentOneToTenYears_0C51C62E1126EA282955E10FBB486E6B" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_LeaseFeePercentageOfRentElevenToTwentyYears" xlink:label="loc_alx_LeaseFeePercentageOfRentElevenToTwentyYears_2D72A0CA05D3432FC361E10FBB487DEA" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_LeaseFeePercentageOfRentElevenToTwentyYears_2D72A0CA05D3432FC361E10FBB487DEA" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_LeaseFeePercentageOfRentTwentyFirstToThirtyYears" xlink:label="loc_alx_LeaseFeePercentageOfRentTwentyFirstToThirtyYears_BB3B6B9C71BE3BD9E80CE10FBB48BFCB" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_LeaseFeePercentageOfRentTwentyFirstToThirtyYears_BB3B6B9C71BE3BD9E80CE10FBB48BFCB" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PercentageIncreaseLeaseFeeIfBrokerUsed" xlink:label="loc_alx_PercentageIncreaseLeaseFeeIfBrokerUsed_9D84CDBBBF5C276B27F6E10FBB49CEE0" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_PercentageIncreaseLeaseFeeIfBrokerUsed_9D84CDBBBF5C276B27F6E10FBB49CEE0" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PercentageCommissionsOnSaleOfAssetsUnderFiftyMillion" xlink:label="loc_alx_PercentageCommissionsOnSaleOfAssetsUnderFiftyMillion_F48CDFE6DAA1BF446A3EE10FBB49137C" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_PercentageCommissionsOnSaleOfAssetsUnderFiftyMillion_F48CDFE6DAA1BF446A3EE10FBB49137C" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_AssetSaleCommissionThreshold" xlink:label="loc_alx_AssetSaleCommissionThreshold_34EF2666A28B98F0ABBDE10FBB496FE3" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_AssetSaleCommissionThreshold_34EF2666A28B98F0ABBDE10FBB496FE3" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PercentageCommissionsOnSaleOfAssetsOverFiftyMillion" xlink:label="loc_alx_PercentageCommissionsOnSaleOfAssetsOverFiftyMillion_74D9233AE38A9A29D486E10FBB49ACB5" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_alx_PercentageCommissionsOnSaleOfAssetsOverFiftyMillion_74D9233AE38A9A29D486E10FBB49ACB5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionDueFromToRelatedParty" xlink:label="loc_us-gaap_RelatedPartyTransactionDueFromToRelatedParty_9E67C9B143DBC5537051E10FBB49F3D0" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B1ADE7465B8A969B24EAE10FBB47A0FB" xlink:to="loc_us-gaap_RelatedPartyTransactionDueFromToRelatedParty_9E67C9B143DBC5537051E10FBB49F3D0" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RelatedPartyTransactionsSummaryOfFeesToVornadoDetail" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_83650D3A1FD1CD6B599BE10FBB61629C" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_08221649EE752F9F9781E10FBB5F1D5D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_83650D3A1FD1CD6B599BE10FBB61629C" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_08221649EE752F9F9781E10FBB5F1D5D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_AA68718622C3CE5C46C3E10FBB5F4E1A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_08221649EE752F9F9781E10FBB5F1D5D" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_AA68718622C3CE5C46C3E10FBB5F4E1A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_FA969532B44ADB2666BAE10FBB5FE8B7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_AA68718622C3CE5C46C3E10FBB5F4E1A" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_FA969532B44ADB2666BAE10FBB5FE8B7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_FA969532B44ADB2666BAE10FBB5FE8B7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_AA68718622C3CE5C46C3E10FBB5F4E1A" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_FA969532B44ADB2666BAE10FBB5FE8B7" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_CompanyManagementFeesMember" xlink:label="loc_alx_CompanyManagementFeesMember_7C3727F574ECD307FD83E10FBB60AC75" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_FA969532B44ADB2666BAE10FBB5FE8B7" xlink:to="loc_alx_CompanyManagementFeesMember_7C3727F574ECD307FD83E10FBB60AC75" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_DevelopmentFeesMember" xlink:label="loc_alx_DevelopmentFeesMember_07111F98DCDB2CF4AD91E10FBB60E75A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_FA969532B44ADB2666BAE10FBB5FE8B7" xlink:to="loc_alx_DevelopmentFeesMember_07111F98DCDB2CF4AD91E10FBB60E75A" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_LeasingFeesMember" xlink:label="loc_alx_LeasingFeesMember_AE1B861643DA71885053E10FBB60AA3D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_FA969532B44ADB2666BAE10FBB5FE8B7" xlink:to="loc_alx_LeasingFeesMember_AE1B861643DA71885053E10FBB60AA3D" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_PropertyManagementFeesMember" xlink:label="loc_alx_PropertyManagementFeesMember_E386988A3DB799B3313EE10FBB603760" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_FA969532B44ADB2666BAE10FBB5FE8B7" xlink:to="loc_alx_PropertyManagementFeesMember_E386988A3DB799B3313EE10FBB603760" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_17F7C457F75CC4CF3496E10FBB603E3F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_08221649EE752F9F9781E10FBB5F1D5D" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_17F7C457F75CC4CF3496E10FBB603E3F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_C744812850685B7A1F32E10FBB61FA25_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_17F7C457F75CC4CF3496E10FBB603E3F" xlink:to="loc_us-gaap_RelatedPartyDomain_C744812850685B7A1F32E10FBB61FA25_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_C744812850685B7A1F32E10FBB61FA25" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_17F7C457F75CC4CF3496E10FBB603E3F" xlink:to="loc_us-gaap_RelatedPartyDomain_C744812850685B7A1F32E10FBB61FA25" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_AffiliatedEntityMember" xlink:label="loc_srt_AffiliatedEntityMember_5E13C9C196638F920D8EE10FBB61FD52" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_C744812850685B7A1F32E10FBB61FA25" xlink:to="loc_srt_AffiliatedEntityMember_5E13C9C196638F920D8EE10FBB61FD52" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty" xlink:label="loc_us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty_5FA405488A1C1AC4C1F4E10FBB612860" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_83650D3A1FD1CD6B599BE10FBB61629C" xlink:to="loc_us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty_5FA405488A1C1AC4C1F4E10FBB612860" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RelatedPartyTransactionsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RevenueRecognition" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RevenueRecognitionComponentsOfLeaseRevenueDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RevenueRecognitionDisaggregationOfRevenueDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_1E53BAD8C04A6EA4B6BFE10FBC74A95E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_8BD94C4E1EA362320967E10FBC730265" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_1E53BAD8C04A6EA4B6BFE10FBC74A95E" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_8BD94C4E1EA362320967E10FBC730265" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srt_ProductOrServiceAxis_71C7A4C134D14AEDC259E10FBC736096" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_8BD94C4E1EA362320967E10FBC730265" xlink:to="loc_srt_ProductOrServiceAxis_71C7A4C134D14AEDC259E10FBC736096" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srt_ProductsAndServicesDomain_FEDBA8940C90966B3B34E10FBC732EC3_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_71C7A4C134D14AEDC259E10FBC736096" xlink:to="loc_srt_ProductsAndServicesDomain_FEDBA8940C90966B3B34E10FBC732EC3_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srt_ProductsAndServicesDomain_FEDBA8940C90966B3B34E10FBC732EC3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_71C7A4C134D14AEDC259E10FBC736096" xlink:to="loc_srt_ProductsAndServicesDomain_FEDBA8940C90966B3B34E10FBC732EC3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ParkingMember" xlink:label="loc_us-gaap_ParkingMember_0E408D5A881DBFE8AE8AE10FBC73BFF3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_FEDBA8940C90966B3B34E10FBC732EC3" xlink:to="loc_us-gaap_ParkingMember_0E408D5A881DBFE8AE8AE10FBC73BFF3" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_DirectServicesMember" xlink:label="loc_alx_DirectServicesMember_15E6C24E3DA8CD565A99E10FBC74F676" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_FEDBA8940C90966B3B34E10FBC732EC3" xlink:to="loc_alx_DirectServicesMember_15E6C24E3DA8CD565A99E10FBC74F676" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseLeaseIncome" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome_086B363A0EA5F9DE5342E10FBC74B9C5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_1E53BAD8C04A6EA4B6BFE10FBC74A95E" xlink:to="loc_us-gaap_OperatingLeaseLeaseIncome_086B363A0EA5F9DE5342E10FBC74B9C5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_DCB884BBC7ACEBA6B2FAE10FBC757333" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_1E53BAD8C04A6EA4B6BFE10FBC74A95E" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_DCB884BBC7ACEBA6B2FAE10FBC757333" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_6B79AE470E2FA43F128DE10FBC75E942" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_1E53BAD8C04A6EA4B6BFE10FBC74A95E" xlink:to="loc_us-gaap_Revenues_6B79AE470E2FA43F128DE10FBC75E942" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RevenueRecognitionNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_8C695769F826BF52595CE10FBB70EFE7" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_2882C4B6D4C711F60EB3E10FBB6E2AF3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_8C695769F826BF52595CE10FBB70EFE7" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_2882C4B6D4C711F60EB3E10FBB6E2AF3" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_0B5D083E2430921A4EBBE10FBB6E4627" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_2882C4B6D4C711F60EB3E10FBB6E2AF3" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_0B5D083E2430921A4EBBE10FBB6E4627" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_9716BFCE5F1B2A8447CAE10FBB6E44E6_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_0B5D083E2430921A4EBBE10FBB6E4627" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_9716BFCE5F1B2A8447CAE10FBB6E44E6_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_9716BFCE5F1B2A8447CAE10FBB6E44E6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_0B5D083E2430921A4EBBE10FBB6E4627" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_9716BFCE5F1B2A8447CAE10FBB6E44E6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_9A4BA33F43181EB7A8F1E10FBB6E1011" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_9716BFCE5F1B2A8447CAE10FBB6E44E6" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_9A4BA33F43181EB7A8F1E10FBB6E1011" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_47133C295AD3F4DB39D6E10FBB6FC480" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_2882C4B6D4C711F60EB3E10FBB6E2AF3" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_47133C295AD3F4DB39D6E10FBB6FC480" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_5A7AF437017F9AD62A17E10FBB6F0743_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_47133C295AD3F4DB39D6E10FBB6FC480" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_5A7AF437017F9AD62A17E10FBB6F0743_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_5A7AF437017F9AD62A17E10FBB6F0743" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_47133C295AD3F4DB39D6E10FBB6FC480" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_5A7AF437017F9AD62A17E10FBB6F0743" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SalesRevenueNetMember" xlink:label="loc_us-gaap_SalesRevenueNetMember_63E5C58A3513E957A3B0E10FBB6F33C2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_5A7AF437017F9AD62A17E10FBB6F0743" xlink:to="loc_us-gaap_SalesRevenueNetMember_63E5C58A3513E957A3B0E10FBB6F33C2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MajorCustomersAxis" xlink:label="loc_srt_MajorCustomersAxis_B67C6760C84F3B8F5D15E10FBB6F62B8" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_2882C4B6D4C711F60EB3E10FBB6E2AF3" xlink:to="loc_srt_MajorCustomersAxis_B67C6760C84F3B8F5D15E10FBB6F62B8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_NameOfMajorCustomerDomain" xlink:label="loc_srt_NameOfMajorCustomerDomain_45D2924EA1325AE93220E10FBB70DCDB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_B67C6760C84F3B8F5D15E10FBB6F62B8" xlink:to="loc_srt_NameOfMajorCustomerDomain_45D2924EA1325AE93220E10FBB70DCDB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_NameOfMajorCustomerDomain" xlink:label="loc_srt_NameOfMajorCustomerDomain_45D2924EA1325AE93220E10FBB70DCDB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_B67C6760C84F3B8F5D15E10FBB6F62B8" xlink:to="loc_srt_NameOfMajorCustomerDomain_45D2924EA1325AE93220E10FBB70DCDB" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_BloombergMember" xlink:label="loc_alx_BloombergMember_39594C5FFA35EEC6FE7CE10FBB70EB10" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_45D2924EA1325AE93220E10FBB70DCDB" xlink:to="loc_alx_BloombergMember_39594C5FFA35EEC6FE7CE10FBB70EB10" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_D59347C5FDC211E52AFDE10FBB70AC23" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_8C695769F826BF52595CE10FBB70EFE7" xlink:to="loc_us-gaap_Revenues_D59347C5FDC211E52AFDE10FBB70AC23" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_17A247326F99B307EA23E10FBB7183C6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_8C695769F826BF52595CE10FBB70EFE7" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_17A247326F99B307EA23E10FBB7183C6" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RevenueRecognitionTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/StockBasedCompensation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/StockBasedCompensationAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22D12B91D21F8EA426D5A051929A0F8A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22D12B91D21F8EA426D5A051929A0F8A" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_42AE6F1B6A416932AC27A051F17A12D8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22D12B91D21F8EA426D5A051929A0F8A" xlink:to="loc_us-gaap_PlanNameAxis_42AE6F1B6A416932AC27A051F17A12D8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_5973CFD3DFD0EEDD10BDA0522D41DD86_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_42AE6F1B6A416932AC27A051F17A12D8" xlink:to="loc_us-gaap_PlanNameDomain_5973CFD3DFD0EEDD10BDA0522D41DD86_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_5973CFD3DFD0EEDD10BDA0522D41DD86" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_42AE6F1B6A416932AC27A051F17A12D8" xlink:to="loc_us-gaap_PlanNameDomain_5973CFD3DFD0EEDD10BDA0522D41DD86" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_A2016OmnibusStockPlanMember" xlink:label="loc_alx_A2016OmnibusStockPlanMember_9D271D5AB46C048460A5A0528DCE5A25" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_5973CFD3DFD0EEDD10BDA0522D41DD86" xlink:to="loc_alx_A2016OmnibusStockPlanMember_9D271D5AB46C048460A5A0528DCE5A25" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_TitleOfIndividualAxis" xlink:label="loc_srt_TitleOfIndividualAxis_F333BE562567CBA52489A051929AFAA3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22D12B91D21F8EA426D5A051929A0F8A" xlink:to="loc_srt_TitleOfIndividualAxis_F333BE562567CBA52489A051929AFAA3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_D27D1FC5525E9F2406D7A051929AC656_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_F333BE562567CBA52489A051929AFAA3" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_D27D1FC5525E9F2406D7A051929AC656_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_D27D1FC5525E9F2406D7A051929AC656" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_F333BE562567CBA52489A051929AFAA3" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_D27D1FC5525E9F2406D7A051929AC656" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_DirectorMember" xlink:label="loc_srt_DirectorMember_FC5B922D29C1B8D8C538A051929B2F3F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_D27D1FC5525E9F2406D7A051929AC656" xlink:to="loc_srt_DirectorMember_FC5B922D29C1B8D8C538A051929B2F3F" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_NewlyAppointedDirectorMember" xlink:label="loc_alx_NewlyAppointedDirectorMember_C549A3A23E9622E96069A051929C0B55" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_D27D1FC5525E9F2406D7A051929AC656" xlink:to="loc_alx_NewlyAppointedDirectorMember_C549A3A23E9622E96069A051929C0B55" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedPerDirector" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedPerDirector_76A404272857559B7C94A051929CF42E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedPerDirector_76A404272857559B7C94A051929CF42E" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsMarketValue" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsMarketValue_03F819B31683D36DC203A051929C6B1A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsMarketValue_03F819B31683D36DC203A051929C6B1A" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValuePerGrant" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValuePerGrant_6437E0D12C62F9907F16A051929C0068" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValuePerGrant_6437E0D12C62F9907F16A051929C0068" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValueTotal" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValueTotal_63EDFDF8A86C40CE61F2A051929C0055" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValueTotal_63EDFDF8A86C40CE61F2A051929C0055" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalNonOptionEquityInstrumentsGrantedPerDirector" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalNonOptionEquityInstrumentsGrantedPerDirector_1F0A52C9CA89C5930345A051929E6C15" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalNonOptionEquityInstrumentsGrantedPerDirector_1F0A52C9CA89C5930345A051929E6C15" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalNonOptionEquityInstrumentsMarketValue" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalNonOptionEquityInstrumentsMarketValue_4FBB75AC21C295B291B7A051929F0A00" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalNonOptionEquityInstrumentsMarketValue_4FBB75AC21C295B291B7A051929F0A00" xlink:type="arc" />
    <link:loc xlink:href="alx-20200630.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalNonOptionEquityInstrumentsGrantDateFairValueTotal" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalNonOptionEquityInstrumentsGrantDateFairValueTotal_8C8E3FDE5ABF5707FEF6A051929F1687" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalNonOptionEquityInstrumentsGrantDateFairValueTotal_8C8E3FDE5ABF5707FEF6A051929F1687" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_96C49123C30F240AFB87A051929FEC79" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_96C49123C30F240AFB87A051929FEC79" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_DE90699B65E62103CE1FA051929FBD33" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AAD58AD6B713A7F72B62A051929CFB68" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_DE90699B65E62103CE1FA051929FBD33" xlink:type="arc" />
  </link:definitionLink>
</link:linkbase>
