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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 TVsT8l46P9B+qmG5nmAozQ==

<SEC-DOCUMENT>0001137439-10-000064.txt : 20100326
<SEC-HEADER>0001137439-10-000064.hdr.sgml : 20100326
<ACCEPTANCE-DATETIME>20100326133752
ACCESSION NUMBER:		0001137439-10-000064
CONFORMED SUBMISSION TYPE:	D/A
PUBLIC DOCUMENT COUNT:		1
ITEM INFORMATION:		Rule 506
ITEM INFORMATION:		Investment Company Act Section 3(c)
ITEM INFORMATION:		Section 3(c)(7)
FILED AS OF DATE:		20100326
DATE AS OF CHANGE:		20100326
EFFECTIVENESS DATE:		20100326

FILER:

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MACKAY MUNICIPAL CREDIT OPPORTUNITIES MASTER FUND LP
		CENTRAL INDEX KEY:			0001460030
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			DE

	FILING VALUES:
		FORM TYPE:		D/A
		SEC ACT:		1933 Act
		SEC FILE NUMBER:	021-129176
		FILM NUMBER:		10707026

	BUSINESS ADDRESS:	
		STREET 1:		100 VILLAGE BLVD
		STREET 2:		SUITE 300
		CITY:			PRINCETON
		STATE:			NJ
		ZIP:			08540
		BUSINESS PHONE:		609-750-8361

	MAIL ADDRESS:	
		STREET 1:		100 VILLAGE BLVD
		STREET 2:		SUITE 300
		CITY:			PRINCETON
		STATE:			NJ
		ZIP:			08540

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	MARINER MUNICIPAL CREDIT OPPORTUNITIES MASTER FUND LP
		DATE OF NAME CHANGE:	20090326
</SEC-HEADER>
<DOCUMENT>
<TYPE>D/A
<SEQUENCE>1
<FILENAME>primary_doc.xml
<TEXT>
<XML>
<?xml version="1.0"?>
<edgarSubmission>

    <schemaVersion>X0603</schemaVersion>

    <submissionType>D/A</submissionType>

    <testOrLive>LIVE</testOrLive>

    <primaryIssuer>
        <cik>0001460030</cik>
        <entityName>MACKAY MUNICIPAL CREDIT OPPORTUNITIES MASTER FUND LP</entityName>
        <issuerAddress>
            <street1>100 VILLAGE BLVD</street1>
            <street2>SUITE 300</street2>
            <city>PRINCETON</city>
            <stateOrCountry>NJ</stateOrCountry>
            <zipCode>08540</zipCode>
        </issuerAddress>
        <issuerPhoneNumber>609-750-8361</issuerPhoneNumber>
        <jurisdictionOfInc>DELAWARE</jurisdictionOfInc>
        <edgarPreviousNameList>
            <previousName>MARINER MUNICIPAL CREDIT OPPORTUNITIES MASTER FUND LP</previousName>
        </edgarPreviousNameList>
        <entityType>Limited Partnership</entityType>
        <yearOfInc>
            <withinFiveYears>true</withinFiveYears>
            <value>2009</value>
        </yearOfInc>
    </primaryIssuer>

    <relatedPersonsList>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>N/A</firstName>
                <lastName>MacKay Municipal Managers Opportunities GP LLC</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>100 Village Blvd.</street1>
                <street2>Suite 300</street2>
                <city>Princeton</city>
                <stateOrCountry>NJ</stateOrCountry>
                <zipCode>08540</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>General Partner (the &quot;General Partner&quot;) of the Issuer</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>John</firstName>
                <middleName>M.</middleName>
                <lastName>Loffredo</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>100 Village Blvd.</street1>
                <street2>Suite 300</street2>
                <city>Princeton</city>
                <stateOrCountry>NJ</stateOrCountry>
                <zipCode>08540</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>Senior Managing Director of MacKay Shields LLC</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Robert</firstName>
                <middleName>A.</middleName>
                <lastName>DiMella</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>100 Village Blvd.</street1>
                <street2>Suite 300</street2>
                <city>Princeton</city>
                <stateOrCountry>NJ</stateOrCountry>
                <zipCode>08540</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>Senior Managing Director of MacKay Shields LLC</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Brain</firstName>
                <middleName>D.</middleName>
                <lastName>Stewart</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>100 Village Blvd.</street1>
                <street2>Suite 300</street2>
                <city>Princeton</city>
                <stateOrCountry>NJ</stateOrCountry>
                <zipCode>08540</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>Managing Director of MacKay Shields LLC</relationshipClarification>
        </relatedPersonInfo>
    </relatedPersonsList>

    <offeringData>
        <industryGroup>
            <industryGroupType>Pooled Investment Fund</industryGroupType>
            <investmentFundInfo>
                <investmentFundType>Other Investment Fund</investmentFundType>
                <is40Act>false</is40Act>
            </investmentFundInfo>
        </industryGroup>
        <issuerSize>
            <aggregateNetAssetValueRange>Decline to Disclose</aggregateNetAssetValueRange>
        </issuerSize>
        <federalExemptionsExclusions>
            <item>06</item>
            <item>3C</item>
            <item>3C.7</item>
        </federalExemptionsExclusions>
        <typeOfFiling>
            <newOrAmendment>
                <isAmendment>true</isAmendment>
                <previousAccessionNumber>9999999997-09-013371</previousAccessionNumber>
            </newOrAmendment>
            <dateOfFirstSale>
                <value>2009-03-01</value>
            </dateOfFirstSale>
        </typeOfFiling>
        <durationOfOffering>
            <moreThanOneYear>true</moreThanOneYear>
        </durationOfOffering>
        <typesOfSecuritiesOffered>
            <isPooledInvestmentFundType>true</isPooledInvestmentFundType>
        </typesOfSecuritiesOffered>
        <businessCombinationTransaction>
            <isBusinessCombinationTransaction>false</isBusinessCombinationTransaction>
            <clarificationOfResponse></clarificationOfResponse>
        </businessCombinationTransaction>
        <minimumInvestmentAccepted>1000000</minimumInvestmentAccepted>
        <salesCompensationList>
            <recipient>
                <recipientName>Mariner Group Capital Markets, Inc.</recipientName>
                <recipientCRDNumber>25878</recipientCRDNumber>
                <associatedBDName>None</associatedBDName>
                <associatedBDCRDNumber>None</associatedBDCRDNumber>
                <recipientAddress>
                    <street1>500 Mamaroneck Avenue</street1>
                    <street2>1st Floor</street2>
                    <city>Harrison</city>
                    <stateOrCountry>NY</stateOrCountry>
                    <zipCode>10528</zipCode>
                </recipientAddress>
                <statesOfSolicitationList>
                    <value>All States</value>
                </statesOfSolicitationList>
            </recipient>
        </salesCompensationList>
        <offeringSalesAmounts>
            <totalOfferingAmount>Indefinite</totalOfferingAmount>
            <totalAmountSold>0</totalAmountSold>
            <totalRemaining>Indefinite</totalRemaining>
            <clarificationOfResponse>This figure has been calculated from inception through February 28, 2010.</clarificationOfResponse>
        </offeringSalesAmounts>
        <investors>
            <hasNonAccreditedInvestors>false</hasNonAccreditedInvestors>
            <totalNumberAlreadyInvested>0</totalNumberAlreadyInvested>
        </investors>
        <salesCommissionsFindersFees>
            <salesCommissions>
                <dollarAmount>0</dollarAmount>
                <isEstimate>true</isEstimate>
            </salesCommissions>
            <findersFees>
                <dollarAmount>0</dollarAmount>
                <isEstimate>true</isEstimate>
            </findersFees>
            <clarificationOfResponse></clarificationOfResponse>
        </salesCommissionsFindersFees>
        <useOfProceeds>
            <grossProceedsUsed>
                <dollarAmount>0</dollarAmount>
            </grossProceedsUsed>
            <clarificationOfResponse></clarificationOfResponse>
        </useOfProceeds>
        <signatureBlock>
            <authorizedRepresentative>false</authorizedRepresentative>
            <signature>
                <issuerName>MACKAY MUNICIPAL CREDIT OPPORTUNITIES MASTER FUND LP</issuerName>
                <signatureName>/s/John M. Loffredo</signatureName>
                <nameOfSigner>John M. Loffredo</nameOfSigner>
                <signatureTitle>Senior Managing Director of MacKay Shields LLC</signatureTitle>
                <signatureDate>2010-03-25</signatureDate>
            </signature>
        </signatureBlock>
    </offeringData>
</edgarSubmission>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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