<?xml version="1.0"?>
<edgarSubmission>

    <schemaVersion>X0708</schemaVersion>

    <submissionType>D</submissionType>

    <testOrLive>LIVE</testOrLive>

    <primaryIssuer>
        <cik>0001757517</cik>
        <entityName>Brookside Mezzanine Fund IV, L.P.</entityName>
        <issuerAddress>
            <street1>201 TRESSER BOULEVARD</street1>
            <street2>SUITE 330</street2>
            <city>STAMFORD</city>
            <stateOrCountry>CT</stateOrCountry>
            <stateOrCountryDescription>CONNECTICUT</stateOrCountryDescription>
            <zipCode>06901</zipCode>
        </issuerAddress>
        <issuerPhoneNumber>(203)595-4532</issuerPhoneNumber>
        <jurisdictionOfInc>DELAWARE</jurisdictionOfInc>
        <issuerPreviousNameList>
            <value>None</value>
        </issuerPreviousNameList>
        <edgarPreviousNameList>
            <value>None</value>
        </edgarPreviousNameList>
        <entityType>Limited Partnership</entityType>
        <yearOfInc>
            <withinFiveYears>true</withinFiveYears>
            <value>2017</value>
        </yearOfInc>
    </primaryIssuer>

    <relatedPersonsList>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>N/A</firstName>
                <lastName>Brookside Mezzanine Partners IV, LLC</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>201 Tresser Boulevard</street1>
                <street2>Suite 330</street2>
                <city>Stamford</city>
                <stateOrCountry>CT</stateOrCountry>
                <stateOrCountryDescription>CONNECTICUT</stateOrCountryDescription>
                <zipCode>06901</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>General Partner</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Devon</firstName>
                <middleName>C.</middleName>
                <lastName>Burger</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>201 Tresser Boulevard</street1>
                <street2>Suite 330</street2>
                <city>Stamford</city>
                <stateOrCountry>CT</stateOrCountry>
                <stateOrCountryDescription>CONNECTICUT</stateOrCountryDescription>
                <zipCode>06901</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>Member of the General Partner</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Gregory</firstName>
                <middleName>C.</middleName>
                <lastName>Foy</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>201 Tresser Boulevard</street1>
                <street2>Suite 330</street2>
                <city>Stamford</city>
                <stateOrCountry>CT</stateOrCountry>
                <stateOrCountryDescription>CONNECTICUT</stateOrCountryDescription>
                <zipCode>06901</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>Member of the General Partner</relationshipClarification>
        </relatedPersonInfo>
    </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>06b</item>
            <item>3C</item>
            <item>3C.1</item>
        </federalExemptionsExclusions>
        <typeOfFiling>
            <newOrAmendment>
                <isAmendment>false</isAmendment>
            </newOrAmendment>
            <dateOfFirstSale>
                <value>2018-10-22</value>
            </dateOfFirstSale>
        </typeOfFiling>
        <durationOfOffering>
            <moreThanOneYear>false</moreThanOneYear>
        </durationOfOffering>
        <typesOfSecuritiesOffered>
            <isPooledInvestmentFundType>true</isPooledInvestmentFundType>
        </typesOfSecuritiesOffered>
        <businessCombinationTransaction>
            <isBusinessCombinationTransaction>false</isBusinessCombinationTransaction>
            <clarificationOfResponse></clarificationOfResponse>
        </businessCombinationTransaction>
        <minimumInvestmentAccepted>0</minimumInvestmentAccepted>
        <salesCompensationList>
            <recipient>
                <recipientName>Equus Financial Consulting</recipientName>
                <recipientCRDNumber>131449</recipientCRDNumber>
                <associatedBDName>None</associatedBDName>
                <associatedBDCRDNumber>None</associatedBDCRDNumber>
                <recipientAddress>
                    <street1>78 Pine St.</street1>
                    <street2>Suite 101</street2>
                    <city>New Canaan</city>
                    <stateOrCountry>CT</stateOrCountry>
                    <stateOrCountryDescription>CONNECTICUT</stateOrCountryDescription>
                    <zipCode>06840</zipCode>
                </recipientAddress>
                <statesOfSolicitationList>
                    <state>OH</state>
                    <description>OHIO</description>
                </statesOfSolicitationList>
                <foreignSolicitation>false</foreignSolicitation>
            </recipient>
            <recipient>
                <recipientName>Keith Stock</recipientName>
                <recipientCRDNumber>6141019</recipientCRDNumber>
                <associatedBDName>Sword Securities LLC</associatedBDName>
                <associatedBDCRDNumber>32244</associatedBDCRDNumber>
                <recipientAddress>
                    <street1>201 Tresser Blvd.</street1>
                    <street2>Suite 345</street2>
                    <city>Stamford</city>
                    <stateOrCountry>CT</stateOrCountry>
                    <stateOrCountryDescription>CONNECTICUT</stateOrCountryDescription>
                    <zipCode>06901</zipCode>
                </recipientAddress>
                <statesOfSolicitationList>
                    <state>GA</state>
                    <description>GEORGIA</description>
                    <state>CT</state>
                    <description>CONNECTICUT</description>
                </statesOfSolicitationList>
                <foreignSolicitation>false</foreignSolicitation>
            </recipient>
        </salesCompensationList>
        <offeringSalesAmounts>
            <totalOfferingAmount>Indefinite</totalOfferingAmount>
            <totalAmountSold>155950000</totalAmountSold>
            <totalRemaining>Indefinite</totalRemaining>
            <clarificationOfResponse></clarificationOfResponse>
        </offeringSalesAmounts>
        <investors>
            <hasNonAccreditedInvestors>false</hasNonAccreditedInvestors>
            <totalNumberAlreadyInvested>70</totalNumberAlreadyInvested>
        </investors>
        <salesCommissionsFindersFees>
            <salesCommissions>
                <dollarAmount>123000</dollarAmount>
                <isEstimate>true</isEstimate>
            </salesCommissions>
            <findersFees>
                <dollarAmount>0</dollarAmount>
                <isEstimate>true</isEstimate>
            </findersFees>
            <clarificationOfResponse></clarificationOfResponse>
        </salesCommissionsFindersFees>
        <useOfProceeds>
            <grossProceedsUsed>
                <dollarAmount>0</dollarAmount>
                <isEstimate>true</isEstimate>
            </grossProceedsUsed>
            <clarificationOfResponse>The management company will receive management fees in an amount based off of the amount of securities sold.</clarificationOfResponse>
        </useOfProceeds>
        <signatureBlock>
            <authorizedRepresentative>false</authorizedRepresentative>
            <signature>
                <issuerName>Brookside Mezzanine Fund IV, L.P.</issuerName>
                <signatureName>Corey L. Sclar</signatureName>
                <nameOfSigner>Corey L. Sclar</nameOfSigner>
                <signatureTitle>Member of the General Partner</signatureTitle>
                <signatureDate>2018-10-31</signatureDate>
            </signature>
        </signatureBlock>
    </offeringData>
</edgarSubmission>
