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<edgarSubmission>

    <schemaVersion>X0603</schemaVersion>

    <submissionType>D</submissionType>

    <testOrLive>LIVE</testOrLive>

    <primaryIssuer>
        <cik>0001485993</cik>
        <entityName>HarbourVest IX-Cayman Buyout Fund L.P.</entityName>
        <issuerAddress>
            <street1>HarbourVest Partners, LLC</street1>
            <street2>One Financial Center, 44th Floor</street2>
            <city>Boston</city>
            <stateOrCountry>MA</stateOrCountry>
            <zipCode>02111</zipCode>
        </issuerAddress>
        <issuerPhoneNumber>617-348-3707</issuerPhoneNumber>
        <jurisdictionOfInc>CAYMAN ISLANDS</jurisdictionOfInc>
        <issuerPreviousNameList>
            <value>None</value>
        </issuerPreviousNameList>
        <edgarPreviousNameList>
            <value>None</value>
        </edgarPreviousNameList>
        <entityType>Limited Partnership</entityType>
        <yearOfInc>
            <withinFiveYears>true</withinFiveYears>
            <value>2009</value>
        </yearOfInc>
    </primaryIssuer>

    <relatedPersonsList>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>n/a</firstName>
                <lastName>HarbourVest IX-Buyout Associates LLC</lastName>
            </relatedPersonName>
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                <street1>HarbourVest Partners, LLC</street1>
                <street2>One Financial Center, 44th Floor</street2>
                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <zipCode>02111</zipCode>
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            <relatedPersonRelationshipList>
                <relationship>Promoter</relationship>
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            <relationshipClarification></relationshipClarification>
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        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Edward</firstName>
                <middleName>W.</middleName>
                <lastName>Kane</lastName>
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                <street1>HarbourVest Partners, LLC</street1>
                <street2>One Financial Center, 44th Floor</street2>
                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <zipCode>02111</zipCode>
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            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
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            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
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        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>D.</firstName>
                <middleName>Brooks</middleName>
                <lastName>Zug</lastName>
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            <relatedPersonAddress>
                <street1>HarbourVest Partners, LLC</street1>
                <street2>One Financial Center, 44th Floor</street2>
                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <zipCode>02111</zipCode>
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            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
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            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
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        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>George</firstName>
                <middleName>R.</middleName>
                <lastName>Anson</lastName>
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            <relatedPersonAddress>
                <street1>HarbourVest Partners (U.K.) Limited</street1>
                <street2>Berkeley Square House, 8 Fl. Berkeley Sq</street2>
                <city>London</city>
                <stateOrCountry>X0</stateOrCountry>
                <zipCode>W1J 6DB</zipCode>
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            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
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            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
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        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Philip</firstName>
                <middleName>M.</middleName>
                <lastName>Bilden</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>HarbourVest Partners (Asia) Limited</street1>
                <street2>Citibank Tower Ste1207 3GardenRdCentral</street2>
                <city>Hong Kong</city>
                <stateOrCountry>K3</stateOrCountry>
                <zipCode>00000</zipCode>
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            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
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            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
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        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>John</firstName>
                <middleName>M.</middleName>
                <lastName>Begg</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>HarbourVest Partners, LLC</street1>
                <street2>One Financial Center, 44th Floor</street2>
                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <zipCode>02111</zipCode>
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            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
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            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
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        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Robert</firstName>
                <middleName>M.</middleName>
                <lastName>Wadsworth</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>HarbourVest Partners, LLC</street1>
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                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <zipCode>02111</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>William</firstName>
                <middleName>A.</middleName>
                <lastName>Johnston</lastName>
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            <relatedPersonAddress>
                <street1>HarbourVest Partners, LLC</street1>
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                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <zipCode>02111</zipCode>
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            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Frederick</firstName>
                <middleName>C.</middleName>
                <lastName>Maynard</lastName>
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            <relatedPersonAddress>
                <street1>HarbourVest Partners, LLC</street1>
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                <zipCode>02111</zipCode>
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            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
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        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Ofer</firstName>
                <lastName>Nemirovsky</lastName>
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            <relatedPersonAddress>
                <street1>HarbourVest Partners, LLC</street1>
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                <zipCode>02111</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
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            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Martha</firstName>
                <middleName>D.</middleName>
                <lastName>Vorlicek</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>HarbourVest Partners, LLC</street1>
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                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <zipCode>02111</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>John</firstName>
                <middleName>G.</middleName>
                <lastName>Morris</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>HarbourVest Partners, LLC</street1>
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                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <zipCode>02111</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Gregory</firstName>
                <middleName>V.</middleName>
                <lastName>Stento</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>HarbourVest Partners, LLC</street1>
                <street2>One Financial Center, 44th Floor</street2>
                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <zipCode>02111</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
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            <relationshipClarification>of the Managing Member of the General Partner (or its affiliates)</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Peter</firstName>
                <middleName>G.</middleName>
                <lastName>Wilson</lastName>
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            <relatedPersonAddress>
                <street1>HarbourVest Partners (U.K.) Limited</street1>
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                <stateOrCountry>X0</stateOrCountry>
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            <relatedPersonRelationshipList>
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        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Michael</firstName>
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            <relatedPersonAddress>
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        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Kathleen</firstName>
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                <lastName>Bacon</lastName>
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                <zipCode>02111</zipCode>
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        <relatedPersonInfo>
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        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>John</firstName>
                <middleName>M.</middleName>
                <lastName>Toomey, Jr.</lastName>
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    </relatedPersonsList>

    <offeringData>
        <industryGroup>
            <industryGroupType>Pooled Investment Fund</industryGroupType>
            <investmentFundInfo>
                <investmentFundType>Private Equity Fund</investmentFundType>
                <is40Act>false</is40Act>
            </investmentFundInfo>
        </industryGroup>
        <issuerSize>
            <revenueRange>Decline to Disclose</revenueRange>
        </issuerSize>
        <federalExemptionsExclusions>
            <item>06</item>
            <item>3C</item>
            <item>3C.7</item>
        </federalExemptionsExclusions>
        <typeOfFiling>
            <newOrAmendment>
                <isAmendment>false</isAmendment>
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            <dateOfFirstSale>
                <yetToOccur>true</yetToOccur>
            </dateOfFirstSale>
        </typeOfFiling>
        <durationOfOffering>
            <moreThanOneYear>true</moreThanOneYear>
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        <typesOfSecuritiesOffered>
            <isEquityType>true</isEquityType>
            <isPooledInvestmentFundType>true</isPooledInvestmentFundType>
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        <businessCombinationTransaction>
            <isBusinessCombinationTransaction>false</isBusinessCombinationTransaction>
            <clarificationOfResponse></clarificationOfResponse>
        </businessCombinationTransaction>
        <minimumInvestmentAccepted>0</minimumInvestmentAccepted>
        <salesCompensationList>
            <recipient>
                <recipientName>Not Applicable</recipientName>
                <recipientCRDNumber>None</recipientCRDNumber>
                <associatedBDName>Warburg Alternative Investments AG</associatedBDName>
                <associatedBDCRDNumber>None</associatedBDCRDNumber>
                <recipientAddress>
                    <street1>Borsenstrasse 26</street1>
                    <city>Zurich</city>
                    <stateOrCountry>V8</stateOrCountry>
                    <zipCode>CH-8001</zipCode>
                </recipientAddress>
                <statesOfSolicitationList></statesOfSolicitationList>
            </recipient>
            <recipient>
                <recipientName>Eliot Kalter</recipientName>
                <recipientCRDNumber>None</recipientCRDNumber>
                <associatedBDName>EM Strategies, Inc.</associatedBDName>
                <associatedBDCRDNumber>None</associatedBDCRDNumber>
                <recipientAddress>
                    <street1>1042 31Street, N.W.</street1>
                    <city>Washington</city>
                    <stateOrCountry>DC</stateOrCountry>
                    <zipCode>20007</zipCode>
                </recipientAddress>
                <statesOfSolicitationList></statesOfSolicitationList>
            </recipient>
        </salesCompensationList>
        <offeringSalesAmounts>
            <totalOfferingAmount>Indefinite</totalOfferingAmount>
            <totalAmountSold>0</totalAmountSold>
            <totalRemaining>Indefinite</totalRemaining>
            <clarificationOfResponse></clarificationOfResponse>
        </offeringSalesAmounts>
        <investors>
            <hasNonAccreditedInvestors>false</hasNonAccreditedInvestors>
            <totalNumberAlreadyInvested>0</totalNumberAlreadyInvested>
        </investors>
        <salesCommissionsFindersFees>
            <salesCommissions>
                <dollarAmount>1000000</dollarAmount>
                <isEstimate>true</isEstimate>
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            <findersFees>
                <dollarAmount>0</dollarAmount>
                <isEstimate>true</isEstimate>
            </findersFees>
            <clarificationOfResponse>The placement agents may be paid for soliciting investors for this feeder fund or its master fund.</clarificationOfResponse>
        </salesCommissionsFindersFees>
        <useOfProceeds>
            <grossProceedsUsed>
                <dollarAmount>0</dollarAmount>
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            <clarificationOfResponse></clarificationOfResponse>
        </useOfProceeds>
        <signatureBlock>
            <authorizedRepresentative>false</authorizedRepresentative>
            <signature>
                <issuerName>HarbourVest IX-Cayman Buyout Fund L.P.</issuerName>
                <signatureName>/s/ Martha D. Vorlicek</signatureName>
                <nameOfSigner>Martha D. Vorlicek</nameOfSigner>
                <signatureTitle>Managing Director of managing member of GP</signatureTitle>
                <signatureDate>2010-02-24</signatureDate>
            </signature>
        </signatureBlock>
    </offeringData>
</edgarSubmission>
