<?xml version="1.0" encoding="us-ascii"?>
<!--XBRL document created by RR Donnelley IM Processor 6.0.0.0 using Fujitsu Interstage XWand-->
<schema targetNamespace="http://www.loomissayles.com/20130128" elementFormDefault="qualified" xmlns="http://www.w3.org/2001/XMLSchema" xmlns:lsf1="http://www.loomissayles.com/20130128" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:nonnum="http://www.xbrl.org/dtr/type/non-numeric">
  <annotation>
    <appinfo>
      <link:linkbaseRef xlink:type="simple" xlink:href="lsf1-20130128_pre.xml" xlink:title="Presentation Links, all" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="lsf1-20130128_cal.xml" xlink:title="Calculation Links, all" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="lsf1-20130128_def.xml" xlink:title="Definition Links, all" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="lsf1-20130128_lab.xml" xlink:title="Label Links, all" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentDocumentandEntityInformation" id="DocumentDocumentandEntityInformation">
        <link:definition>000000 - Document - Document and Entity Information</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnSummaryUnlabeledLoomisSaylesGlobalEquityandIncomeFund" id="DocumentRiskReturnSummaryUnlabeledLoomisSaylesGlobalEquityandIncomeFund">
        <link:definition>000011 - Document - Risk/Return Summary {Unlabeled} - Loomis Sayles Global Equity and Income Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleShareholderFeesLoomisSaylesGlobalEquityandIncomeFund" id="ScheduleShareholderFeesLoomisSaylesGlobalEquityandIncomeFund">
        <link:definition>000012 - Schedule - Shareholder Fees {- Loomis Sayles Global Equity and Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesGlobalEquityandIncomeFund" id="ScheduleAnnualFundOperatingExpensesLoomisSaylesGlobalEquityandIncomeFund">
        <link:definition>000013 - Schedule - Annual Fund Operating Expenses {- Loomis Sayles Global Equity and Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesGlobalEquityandIncomeFund" id="ScheduleExpenseExampleTransposedLoomisSaylesGlobalEquityandIncomeFund">
        <link:definition>000014 - Schedule - Expense Example {Transposed} {- Loomis Sayles Global Equity and Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesGlobalEquityandIncomeFund" id="ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesGlobalEquityandIncomeFund">
        <link:definition>000015 - Schedule - Expense Example, No Redemption {Transposed} {- Loomis Sayles Global Equity and Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesGlobalEquityandIncomeFundBarChart" id="ScheduleAnnualTotalReturnsLoomisSaylesGlobalEquityandIncomeFundBarChart">
        <link:definition>000016 - Schedule - Annual Total Returns - Loomis Sayles Global Equity and Income Fund [BarChart]</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesGlobalEquityandIncomeFund" id="ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesGlobalEquityandIncomeFund">
        <link:definition>000017 - Schedule - Average Annual Total Returns {Transposed} {- Loomis Sayles Global Equity and Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnDetailUnlabeledLoomisSaylesGlobalEquityandIncomeFund" id="DocumentRiskReturnDetailUnlabeledLoomisSaylesGlobalEquityandIncomeFund">
        <link:definition>000018 - Document - Risk/Return Detail {Unlabeled} - Loomis Sayles Global Equity and Income Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DisclosureRiskReturnDetailDataElementsLoomisSaylesGlobalEquityandIncomeFund" id="DisclosureRiskReturnDetailDataElementsLoomisSaylesGlobalEquityandIncomeFund">
        <link:definition>000019 - Disclosure - Risk/Return Detail Data {Elements} - Loomis Sayles Global Equity and Income Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnSummaryUnlabeledLoomisSaylesGrowthFund" id="DocumentRiskReturnSummaryUnlabeledLoomisSaylesGrowthFund">
        <link:definition>000021 - Document - Risk/Return Summary {Unlabeled} - Loomis Sayles Growth Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleShareholderFeesLoomisSaylesGrowthFund" id="ScheduleShareholderFeesLoomisSaylesGrowthFund">
        <link:definition>000022 - Schedule - Shareholder Fees {- Loomis Sayles Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesGrowthFund" id="ScheduleAnnualFundOperatingExpensesLoomisSaylesGrowthFund">
        <link:definition>000023 - Schedule - Annual Fund Operating Expenses {- Loomis Sayles Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesGrowthFund" id="ScheduleExpenseExampleTransposedLoomisSaylesGrowthFund">
        <link:definition>000024 - Schedule - Expense Example {Transposed} {- Loomis Sayles Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesGrowthFund" id="ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesGrowthFund">
        <link:definition>000025 - Schedule - Expense Example, No Redemption {Transposed} {- Loomis Sayles Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesGrowthFundBarChart" id="ScheduleAnnualTotalReturnsLoomisSaylesGrowthFundBarChart">
        <link:definition>000026 - Schedule - Annual Total Returns - Loomis Sayles Growth Fund [BarChart]</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesGrowthFund" id="ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesGrowthFund">
        <link:definition>000027 - Schedule - Average Annual Total Returns {Transposed} {- Loomis Sayles Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnDetailUnlabeledLoomisSaylesGrowthFund" id="DocumentRiskReturnDetailUnlabeledLoomisSaylesGrowthFund">
        <link:definition>000028 - Document - Risk/Return Detail {Unlabeled} - Loomis Sayles Growth Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DisclosureRiskReturnDetailDataElementsLoomisSaylesGrowthFund" id="DisclosureRiskReturnDetailDataElementsLoomisSaylesGrowthFund">
        <link:definition>000029 - Disclosure - Risk/Return Detail Data {Elements} - Loomis Sayles Growth Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnSummaryUnlabeledLoomisSaylesMidCapGrowthFund" id="DocumentRiskReturnSummaryUnlabeledLoomisSaylesMidCapGrowthFund">
        <link:definition>000031 - Document - Risk/Return Summary {Unlabeled} - Loomis Sayles Mid Cap Growth Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleShareholderFeesLoomisSaylesMidCapGrowthFund" id="ScheduleShareholderFeesLoomisSaylesMidCapGrowthFund">
        <link:definition>000032 - Schedule - Shareholder Fees {- Loomis Sayles Mid Cap Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesMidCapGrowthFund" id="ScheduleAnnualFundOperatingExpensesLoomisSaylesMidCapGrowthFund">
        <link:definition>000033 - Schedule - Annual Fund Operating Expenses {- Loomis Sayles Mid Cap Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesMidCapGrowthFund" id="ScheduleExpenseExampleTransposedLoomisSaylesMidCapGrowthFund">
        <link:definition>000034 - Schedule - Expense Example {Transposed} {- Loomis Sayles Mid Cap Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesMidCapGrowthFund" id="ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesMidCapGrowthFund">
        <link:definition>000035 - Schedule - Expense Example, No Redemption {Transposed} {- Loomis Sayles Mid Cap Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesMidCapGrowthFundBarChart" id="ScheduleAnnualTotalReturnsLoomisSaylesMidCapGrowthFundBarChart">
        <link:definition>000036 - Schedule - Annual Total Returns - Loomis Sayles Mid Cap Growth Fund [BarChart]</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesMidCapGrowthFund" id="ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesMidCapGrowthFund">
        <link:definition>000037 - Schedule - Average Annual Total Returns {Transposed} {- Loomis Sayles Mid Cap Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnDetailUnlabeledLoomisSaylesMidCapGrowthFund" id="DocumentRiskReturnDetailUnlabeledLoomisSaylesMidCapGrowthFund">
        <link:definition>000038 - Document - Risk/Return Detail {Unlabeled} - Loomis Sayles Mid Cap Growth Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DisclosureRiskReturnDetailDataElementsLoomisSaylesMidCapGrowthFund" id="DisclosureRiskReturnDetailDataElementsLoomisSaylesMidCapGrowthFund">
        <link:definition>000039 - Disclosure - Risk/Return Detail Data {Elements} - Loomis Sayles Mid Cap Growth Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnSummaryUnlabeledLoomisSaylesValueFund" id="DocumentRiskReturnSummaryUnlabeledLoomisSaylesValueFund">
        <link:definition>000041 - Document - Risk/Return Summary {Unlabeled} - Loomis Sayles Value Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleShareholderFeesLoomisSaylesValueFund" id="ScheduleShareholderFeesLoomisSaylesValueFund">
        <link:definition>000042 - Schedule - Shareholder Fees {- Loomis Sayles Value Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesValueFund" id="ScheduleAnnualFundOperatingExpensesLoomisSaylesValueFund">
        <link:definition>000043 - Schedule - Annual Fund Operating Expenses {- Loomis Sayles Value Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesValueFund" id="ScheduleExpenseExampleTransposedLoomisSaylesValueFund">
        <link:definition>000044 - Schedule - Expense Example {Transposed} {- Loomis Sayles Value Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesValueFund" id="ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesValueFund">
        <link:definition>000045 - Schedule - Expense Example, No Redemption {Transposed} {- Loomis Sayles Value Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesValueFundBarChart" id="ScheduleAnnualTotalReturnsLoomisSaylesValueFundBarChart">
        <link:definition>000046 - Schedule - Annual Total Returns - Loomis Sayles Value Fund [BarChart]</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesValueFund" id="ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesValueFund">
        <link:definition>000047 - Schedule - Average Annual Total Returns {Transposed} {- Loomis Sayles Value Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnDetailUnlabeledLoomisSaylesValueFund" id="DocumentRiskReturnDetailUnlabeledLoomisSaylesValueFund">
        <link:definition>000048 - Document - Risk/Return Detail {Unlabeled} - Loomis Sayles Value Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DisclosureRiskReturnDetailDataElementsLoomisSaylesValueFund" id="DisclosureRiskReturnDetailDataElementsLoomisSaylesValueFund">
        <link:definition>000049 - Disclosure - Risk/Return Detail Data {Elements} - Loomis Sayles Value Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnSummaryUnlabeledLoomisSaylesHighIncomeFund" id="DocumentRiskReturnSummaryUnlabeledLoomisSaylesHighIncomeFund">
        <link:definition>000051 - Document - Risk/Return Summary {Unlabeled} - Loomis Sayles High Income Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleShareholderFeesLoomisSaylesHighIncomeFund" id="ScheduleShareholderFeesLoomisSaylesHighIncomeFund">
        <link:definition>000052 - Schedule - Shareholder Fees {- Loomis Sayles High Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesHighIncomeFund" id="ScheduleAnnualFundOperatingExpensesLoomisSaylesHighIncomeFund">
        <link:definition>000053 - Schedule - Annual Fund Operating Expenses {- Loomis Sayles High Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesHighIncomeFund" id="ScheduleExpenseExampleTransposedLoomisSaylesHighIncomeFund">
        <link:definition>000054 - Schedule - Expense Example {Transposed} {- Loomis Sayles High Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesHighIncomeFund" id="ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesHighIncomeFund">
        <link:definition>000055 - Schedule - Expense Example, No Redemption {Transposed} {- Loomis Sayles High Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesHighIncomeFundBarChart" id="ScheduleAnnualTotalReturnsLoomisSaylesHighIncomeFundBarChart">
        <link:definition>000056 - Schedule - Annual Total Returns - Loomis Sayles High Income Fund [BarChart]</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesHighIncomeFund" id="ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesHighIncomeFund">
        <link:definition>000057 - Schedule - Average Annual Total Returns {Transposed} {- Loomis Sayles High Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnDetailUnlabeledLoomisSaylesHighIncomeFund" id="DocumentRiskReturnDetailUnlabeledLoomisSaylesHighIncomeFund">
        <link:definition>000058 - Document - Risk/Return Detail {Unlabeled} - Loomis Sayles High Income Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DisclosureRiskReturnDetailDataElementsLoomisSaylesHighIncomeFund" id="DisclosureRiskReturnDetailDataElementsLoomisSaylesHighIncomeFund">
        <link:definition>000059 - Disclosure - Risk/Return Detail Data {Elements} - Loomis Sayles High Income Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnSummaryUnlabeledLoomisSaylesInternationalBondFund" id="DocumentRiskReturnSummaryUnlabeledLoomisSaylesInternationalBondFund">
        <link:definition>000061 - Document - Risk/Return Summary {Unlabeled} - Loomis Sayles International Bond Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleShareholderFeesLoomisSaylesInternationalBondFund" id="ScheduleShareholderFeesLoomisSaylesInternationalBondFund">
        <link:definition>000062 - Schedule - Shareholder Fees {- Loomis Sayles International Bond Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesInternationalBondFund" id="ScheduleAnnualFundOperatingExpensesLoomisSaylesInternationalBondFund">
        <link:definition>000063 - Schedule - Annual Fund Operating Expenses {- Loomis Sayles International Bond Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesInternationalBondFund" id="ScheduleExpenseExampleTransposedLoomisSaylesInternationalBondFund">
        <link:definition>000064 - Schedule - Expense Example {Transposed} {- Loomis Sayles International Bond Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesInternationalBondFund" id="ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesInternationalBondFund">
        <link:definition>000065 - Schedule - Expense Example, No Redemption {Transposed} {- Loomis Sayles International Bond Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesInternationalBondFundBarChart" id="ScheduleAnnualTotalReturnsLoomisSaylesInternationalBondFundBarChart">
        <link:definition>000066 - Schedule - Annual Total Returns - Loomis Sayles International Bond Fund [BarChart]</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesInternationalBondFund" id="ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesInternationalBondFund">
        <link:definition>000067 - Schedule - Average Annual Total Returns {Transposed} {- Loomis Sayles International Bond Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnDetailUnlabeledLoomisSaylesInternationalBondFund" id="DocumentRiskReturnDetailUnlabeledLoomisSaylesInternationalBondFund">
        <link:definition>000068 - Document - Risk/Return Detail {Unlabeled} - Loomis Sayles International Bond Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DisclosureRiskReturnDetailDataElementsLoomisSaylesInternationalBondFund" id="DisclosureRiskReturnDetailDataElementsLoomisSaylesInternationalBondFund">
        <link:definition>000069 - Disclosure - Risk/Return Detail Data {Elements} - Loomis Sayles International Bond Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnSummaryUnlabeledLoomisSaylesInvestmentGradeBondFund" id="DocumentRiskReturnSummaryUnlabeledLoomisSaylesInvestmentGradeBondFund">
        <link:definition>000071 - Document - Risk/Return Summary {Unlabeled} - Loomis Sayles Investment Grade Bond Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleShareholderFeesLoomisSaylesInvestmentGradeBondFund" id="ScheduleShareholderFeesLoomisSaylesInvestmentGradeBondFund">
        <link:definition>000072 - Schedule - Shareholder Fees {- Loomis Sayles Investment Grade Bond Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesInvestmentGradeBondFund" id="ScheduleAnnualFundOperatingExpensesLoomisSaylesInvestmentGradeBondFund">
        <link:definition>000073 - Schedule - Annual Fund Operating Expenses {- Loomis Sayles Investment Grade Bond Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesInvestmentGradeBondFund" id="ScheduleExpenseExampleTransposedLoomisSaylesInvestmentGradeBondFund">
        <link:definition>000074 - Schedule - Expense Example {Transposed} {- Loomis Sayles Investment Grade Bond Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesInvestmentGradeBondFund" id="ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesInvestmentGradeBondFund">
        <link:definition>000075 - Schedule - Expense Example, No Redemption {Transposed} {- Loomis Sayles Investment Grade Bond Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesInvestmentGradeBondFundBarChart" id="ScheduleAnnualTotalReturnsLoomisSaylesInvestmentGradeBondFundBarChart">
        <link:definition>000076 - Schedule - Annual Total Returns - Loomis Sayles Investment Grade Bond Fund [BarChart]</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesInvestmentGradeBondFund" id="ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesInvestmentGradeBondFund">
        <link:definition>000077 - Schedule - Average Annual Total Returns {Transposed} {- Loomis Sayles Investment Grade Bond Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnDetailUnlabeledLoomisSaylesInvestmentGradeBondFund" id="DocumentRiskReturnDetailUnlabeledLoomisSaylesInvestmentGradeBondFund">
        <link:definition>000078 - Document - Risk/Return Detail {Unlabeled} - Loomis Sayles Investment Grade Bond Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DisclosureRiskReturnDetailDataElementsLoomisSaylesInvestmentGradeBondFund" id="DisclosureRiskReturnDetailDataElementsLoomisSaylesInvestmentGradeBondFund">
        <link:definition>000079 - Disclosure - Risk/Return Detail Data {Elements} - Loomis Sayles Investment Grade Bond Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnSummaryUnlabeledLoomisSaylesLimitedTermGovernmentandAgencyFund" id="DocumentRiskReturnSummaryUnlabeledLoomisSaylesLimitedTermGovernmentandAgencyFund">
        <link:definition>000081 - Document - Risk/Return Summary {Unlabeled} - Loomis Sayles Limited Term Government and Agency Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleShareholderFeesLoomisSaylesLimitedTermGovernmentandAgencyFund" id="ScheduleShareholderFeesLoomisSaylesLimitedTermGovernmentandAgencyFund">
        <link:definition>000082 - Schedule - Shareholder Fees {- Loomis Sayles Limited Term Government and Agency Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesLimitedTermGovernmentandAgencyFund" id="ScheduleAnnualFundOperatingExpensesLoomisSaylesLimitedTermGovernmentandAgencyFund">
        <link:definition>000083 - Schedule - Annual Fund Operating Expenses {- Loomis Sayles Limited Term Government and Agency Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesLimitedTermGovernmentandAgencyFund" id="ScheduleExpenseExampleTransposedLoomisSaylesLimitedTermGovernmentandAgencyFund">
        <link:definition>000084 - Schedule - Expense Example {Transposed} {- Loomis Sayles Limited Term Government and Agency Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesLimitedTermGovernmentandAgencyFund" id="ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesLimitedTermGovernmentandAgencyFund">
        <link:definition>000085 - Schedule - Expense Example, No Redemption {Transposed} {- Loomis Sayles Limited Term Government and Agency Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesLimitedTermGovernmentandAgencyFundBarChart" id="ScheduleAnnualTotalReturnsLoomisSaylesLimitedTermGovernmentandAgencyFundBarChart">
        <link:definition>000086 - Schedule - Annual Total Returns - Loomis Sayles Limited Term Government and Agency Fund [BarChart]</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesLimitedTermGovernmentandAgencyFund" id="ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesLimitedTermGovernmentandAgencyFund">
        <link:definition>000087 - Schedule - Average Annual Total Returns {Transposed} {- Loomis Sayles Limited Term Government and Agency Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnDetailUnlabeledLoomisSaylesLimitedTermGovernmentandAgencyFund" id="DocumentRiskReturnDetailUnlabeledLoomisSaylesLimitedTermGovernmentandAgencyFund">
        <link:definition>000088 - Document - Risk/Return Detail {Unlabeled} - Loomis Sayles Limited Term Government and Agency Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DisclosureRiskReturnDetailDataElementsLoomisSaylesLimitedTermGovernmentandAgencyFund" id="DisclosureRiskReturnDetailDataElementsLoomisSaylesLimitedTermGovernmentandAgencyFund">
        <link:definition>000089 - Disclosure - Risk/Return Detail Data {Elements} - Loomis Sayles Limited Term Government and Agency Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnSummaryUnlabeledLoomisSaylesStrategicIncomeFund" id="DocumentRiskReturnSummaryUnlabeledLoomisSaylesStrategicIncomeFund">
        <link:definition>000091 - Document - Risk/Return Summary {Unlabeled} - Loomis Sayles Strategic Income Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleShareholderFeesLoomisSaylesStrategicIncomeFund" id="ScheduleShareholderFeesLoomisSaylesStrategicIncomeFund">
        <link:definition>000092 - Schedule - Shareholder Fees {- Loomis Sayles Strategic Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesStrategicIncomeFund" id="ScheduleAnnualFundOperatingExpensesLoomisSaylesStrategicIncomeFund">
        <link:definition>000093 - Schedule - Annual Fund Operating Expenses {- Loomis Sayles Strategic Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesStrategicIncomeFund" id="ScheduleExpenseExampleTransposedLoomisSaylesStrategicIncomeFund">
        <link:definition>000094 - Schedule - Expense Example {Transposed} {- Loomis Sayles Strategic Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesStrategicIncomeFund" id="ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesStrategicIncomeFund">
        <link:definition>000095 - Schedule - Expense Example, No Redemption {Transposed} {- Loomis Sayles Strategic Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesStrategicIncomeFundBarChart" id="ScheduleAnnualTotalReturnsLoomisSaylesStrategicIncomeFundBarChart">
        <link:definition>000096 - Schedule - Annual Total Returns - Loomis Sayles Strategic Income Fund [BarChart]</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesStrategicIncomeFund" id="ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesStrategicIncomeFund">
        <link:definition>000097 - Schedule - Average Annual Total Returns {Transposed} {- Loomis Sayles Strategic Income Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnDetailUnlabeledLoomisSaylesStrategicIncomeFund" id="DocumentRiskReturnDetailUnlabeledLoomisSaylesStrategicIncomeFund">
        <link:definition>000098 - Document - Risk/Return Detail {Unlabeled} - Loomis Sayles Strategic Income Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DisclosureRiskReturnDetailDataElementsLoomisSaylesStrategicIncomeFund" id="DisclosureRiskReturnDetailDataElementsLoomisSaylesStrategicIncomeFund">
        <link:definition>000099 - Disclosure - Risk/Return Detail Data {Elements} - Loomis Sayles Strategic Income Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnSummaryUnlabeledLoomisSaylesSmallCapGrowthFund" id="DocumentRiskReturnSummaryUnlabeledLoomisSaylesSmallCapGrowthFund">
        <link:definition>000101 - Document - Risk/Return Summary {Unlabeled} - Loomis Sayles Small Cap Growth Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleShareholderFeesLoomisSaylesSmallCapGrowthFund" id="ScheduleShareholderFeesLoomisSaylesSmallCapGrowthFund">
        <link:definition>000102 - Schedule - Shareholder Fees {- Loomis Sayles Small Cap Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesSmallCapGrowthFund" id="ScheduleAnnualFundOperatingExpensesLoomisSaylesSmallCapGrowthFund">
        <link:definition>000103 - Schedule - Annual Fund Operating Expenses {- Loomis Sayles Small Cap Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesSmallCapGrowthFund" id="ScheduleExpenseExampleTransposedLoomisSaylesSmallCapGrowthFund">
        <link:definition>000104 - Schedule - Expense Example {Transposed} {- Loomis Sayles Small Cap Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesSmallCapGrowthFund" id="ScheduleExpenseExampleNoRedemptionTransposedLoomisSaylesSmallCapGrowthFund">
        <link:definition>000105 - Schedule - Expense Example, No Redemption {Transposed} {- Loomis Sayles Small Cap Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesSmallCapGrowthFundBarChart" id="ScheduleAnnualTotalReturnsLoomisSaylesSmallCapGrowthFundBarChart">
        <link:definition>000106 - Schedule - Annual Total Returns - Loomis Sayles Small Cap Growth Fund [BarChart]</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesSmallCapGrowthFund" id="ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesSmallCapGrowthFund">
        <link:definition>000107 - Schedule - Average Annual Total Returns {Transposed} {- Loomis Sayles Small Cap Growth Fund}</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DocumentRiskReturnDetailUnlabeledLoomisSaylesSmallCapGrowthFund" id="DocumentRiskReturnDetailUnlabeledLoomisSaylesSmallCapGrowthFund">
        <link:definition>000108 - Document - Risk/Return Detail {Unlabeled} - Loomis Sayles Small Cap Growth Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.loomissayles.com/role/DisclosureRiskReturnDetailDataElementsLoomisSaylesSmallCapGrowthFund" id="DisclosureRiskReturnDetailDataElementsLoomisSaylesSmallCapGrowthFund">
        <link:definition>000109 - Disclosure - Risk/Return Detail Data {Elements} - Loomis Sayles Small Cap Growth Fund</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </appinfo>
  </annotation>
  <import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
  <import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" />
  <import namespace="http://xbrl.sec.gov/rr/2012-01-31" schemaLocation="http://xbrl.sec.gov/rr/2012/rr-2012-01-31.xsd" />
  <import namespace="http://xbrl.sec.gov/dei/2012-01-31" schemaLocation="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd" />
  <import namespace="http://www.xbrl.org/dtr/type/non-numeric" schemaLocation="http://www.xbrl.org/dtr/type/nonNumeric-2009-12-16.xsd" />
  <element name="S000006698Member" id="lsf1_S000006698Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000027670Member" id="lsf1_C000027670Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000027671Member" id="lsf1_C000027671Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018226Member" id="lsf1_C000018226Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="MsciWorldIndexMember" id="lsf1_MsciWorldIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="CitigroupWorldGovernmentBondIndexMember" id="lsf1_CitigroupWorldGovernmentBondIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="S000006699Member" id="lsf1_S000006699Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018227Member" id="lsf1_C000018227Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018228Member" id="lsf1_C000018228Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018229Member" id="lsf1_C000018229Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000125484Member" id="lsf1_C000125484Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018230Member" id="lsf1_C000018230Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="RussellThousandGrowthIndexMember" id="lsf1_RussellThousandGrowthIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="S000006695Member" id="lsf1_S000006695Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018223Member" id="lsf1_C000018223Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000075148Member" id="lsf1_C000075148Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000125482Member" id="lsf1_C000125482Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018222Member" id="lsf1_C000018222Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="RussellMidcapGrowthIndexMember" id="lsf1_RussellMidcapGrowthIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="S000006697Member" id="lsf1_S000006697Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000034548Member" id="lsf1_C000034548Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000049398Member" id="lsf1_C000049398Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000049399Member" id="lsf1_C000049399Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000125483Member" id="lsf1_C000125483Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018225Member" id="lsf1_C000018225Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000082997Member" id="lsf1_C000082997Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="RussellThousandValueIndexMember" id="lsf1_RussellThousandValueIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="S000006700Member" id="lsf1_S000006700Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018231Member" id="lsf1_C000018231Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018232Member" id="lsf1_C000018232Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018233Member" id="lsf1_C000018233Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000069253Member" id="lsf1_C000069253Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="BarclaysUSCorporateHighYieldBondIndexMember" id="lsf1_BarclaysUSCorporateHighYieldBondIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="S000020816Member" id="lsf1_S000020816Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000058150Member" id="lsf1_C000058150Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000058151Member" id="lsf1_C000058151Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000058152Member" id="lsf1_C000058152Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="BarclaysGlobalAggregateExUsdBondIndexMember" id="lsf1_BarclaysGlobalAggregateExUsdBondIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <element name="S000006701Member" id="lsf1_S000006701Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000082998Member" id="lsf1_C000082998Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018234Member" id="lsf1_C000018234Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018235Member" id="lsf1_C000018235Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018236Member" id="lsf1_C000018236Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018237Member" id="lsf1_C000018237Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000125485Member" id="lsf1_C000125485Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018238Member" id="lsf1_C000018238Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="BarclaysUSGovernmentCreditBondIndexMember" id="lsf1_BarclaysUSGovernmentCreditBondIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="S000006702Member" id="lsf1_S000006702Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018239Member" id="lsf1_C000018239Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018240Member" id="lsf1_C000018240Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018241Member" id="lsf1_C000018241Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018242Member" id="lsf1_C000018242Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="BarclaysUsOneFiveYearGovernmentBondIndexMember" id="lsf1_BarclaysUsOneFiveYearGovernmentBondIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="S000006706Member" id="lsf1_S000006706Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000082999Member" id="lsf1_C000082999Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018251Member" id="lsf1_C000018251Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018252Member" id="lsf1_C000018252Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018253Member" id="lsf1_C000018253Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000125487Member" id="lsf1_C000125487Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018254Member" id="lsf1_C000018254Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="BarclaysUsAggregateBondIndexMember" id="lsf1_BarclaysUsAggregateBondIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="BarclaysUsUniversalBondIndexMember" id="lsf1_BarclaysUsUniversalBondIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="S000006705Member" id="lsf1_S000006705Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000125486Member" id="lsf1_C000125486Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018249Member" id="lsf1_C000018249Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="C000018250Member" id="lsf1_C000018250Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="RussellTwoThousandGrowthIndexMember" id="lsf1_RussellTwoThousandGrowthIndexMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
</schema>
