-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 HTBNTWzZR6jx8xJy8l4v+x5//6oqfWYi8MJWavtHCLLAv0KdxqpmA1e4p+9AgGCZ
 ZRSN9NybVTOvJg7/G/Chpw==

<SEC-DOCUMENT>0001193099-10-000054.txt : 20100901
<SEC-HEADER>0001193099-10-000054.hdr.sgml : 20100901
<ACCEPTANCE-DATETIME>20100901212427
ACCESSION NUMBER:		0001193099-10-000054
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100830
FILED AS OF DATE:		20100901
DATE AS OF CHANGE:		20100901

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Klein Peter S
		CENTRAL INDEX KEY:			0001478007

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-14278
		FILM NUMBER:		101053430

	MAIL ADDRESS:	
		STREET 1:		C/O MICROSOFT CORPORATION
		STREET 2:		ONE MICROSOFT WAY
		CITY:			REDMOND
		STATE:			WA
		ZIP:			98052-6399

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MICROSOFT CORP
		CENTRAL INDEX KEY:			0000789019
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-PREPACKAGED SOFTWARE [7372]
		IRS NUMBER:				911144442
		STATE OF INCORPORATION:			WA
		FISCAL YEAR END:			0630

	BUSINESS ADDRESS:	
		STREET 1:		ONE MICROSOFT WAY
		CITY:			REDMOND
		STATE:			WA
		ZIP:			98052-6399
		BUSINESS PHONE:		425-882-8080

	MAIL ADDRESS:	
		STREET 1:		ONE MICROSOFT WAY
		CITY:			REDMOND
		STATE:			WA
		ZIP:			98052-6399
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-08-30</periodOfReport>

    <issuer>
        <issuerCik>0000789019</issuerCik>
        <issuerName>MICROSOFT CORP</issuerName>
        <issuerTradingSymbol>MSFT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001478007</rptOwnerCik>
            <rptOwnerName>Klein Peter S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MICROSOFT CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>ONE MICROSOFT WAY</rptOwnerStreet2>
            <rptOwnerCity>REDMOND</rptOwnerCity>
            <rptOwnerState>WA</rptOwnerState>
            <rptOwnerZipCode>98052-6399</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-08-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1665</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23.93</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>92956</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-08-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>7326</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23.64</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>85630</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes></footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Keith R. Dolliver, Attorney-in-fact for Peter S. Klein</signatureName>
        <signatureDate>2010-09-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----