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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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 3FyUoL7VkP7xoTS9at+sLQ==

<SEC-DOCUMENT>0001104659-06-068824.txt : 20061026
<SEC-HEADER>0001104659-06-068824.hdr.sgml : 20061026
<ACCEPTANCE-DATETIME>20061026134747
ACCESSION NUMBER:		0001104659-06-068824
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20061025
FILED AS OF DATE:		20061026
DATE AS OF CHANGE:		20061026

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Riley Sean P
		CENTRAL INDEX KEY:			0001338874

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-51560
		FILM NUMBER:		061165239

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		952-746-2200

	MAIL ADDRESS:	
		STREET 1:		5900 GREEN OAK DRIVE
		CITY:			MINNEAPOLIS
		STATE:			MN
		ZIP:			55343

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MATHSTAR INC
		CENTRAL INDEX KEY:			0001118037
		STANDARD INDUSTRIAL CLASSIFICATION:	SEMICONDUCTORS & RELATED DEVICES [3674]
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			MN
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		19075 NORTHWEST TANASBOURNE DRIVE
		STREET 2:		SUITE 200
		CITY:			HILLSBORO
		STATE:			OR
		ZIP:			97124
		BUSINESS PHONE:		503-726-5500

	MAIL ADDRESS:	
		STREET 1:		19075 NORTHWEST TANASBOURNE DRIVE
		STREET 2:		SUITE 200
		CITY:			HILLSBORO
		STATE:			OR
		ZIP:			97124
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>a4.xml
<DESCRIPTION>4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-10-25</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001118037</issuerCik>
        <issuerName>MATHSTAR INC</issuerName>
        <issuerTradingSymbol>MATH</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001338874</rptOwnerCik>
            <rptOwnerName>Riley Sean P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>5900 GREEN OAK DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MINNEAPOLIS</rptOwnerCity>
            <rptOwnerState>MN</rptOwnerState>
            <rptOwnerZipCode>55343</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice President of Marketing</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2006-10-25</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>17800</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.9754</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>65534</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Sold pursuant to a 10b5-1 plan.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>James W. Cruckshank, by power of attorney</signatureName>
        <signatureDate>2006-10-26</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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