-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
 MFgwCgYEVQgBAQICAf8DSgAwRwJAW2sNKK9AVtBzYZmr6aGjlWyK3XmZv3dTINen
 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 IT2A1DCKFmIWxCiW9hSqo7RJWwuiUjCZMXTgX6F7vCXh3EBpRmpbO++1GEL8zxOO
 M1w28adbSbG8N/z6m/7smA==

<SEC-DOCUMENT>0001246049-05-000003.txt : 20050404
<SEC-HEADER>0001246049-05-000003.hdr.sgml : 20050404
<ACCEPTANCE-DATETIME>20050404183544
ACCESSION NUMBER:		0001246049-05-000003
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050331
FILED AS OF DATE:		20050404
DATE AS OF CHANGE:		20050404

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ADAPTEC INC
		CENTRAL INDEX KEY:			0000709804
		STANDARD INDUSTRIAL CLASSIFICATION:	COMPUTER COMMUNICATIONS EQUIPMENT [3576]
		IRS NUMBER:				942748530
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0331

	BUSINESS ADDRESS:	
		STREET 1:		691 S MILPITAS BLVD
		STREET 2:		M/S25
		CITY:			MILPITAS
		STATE:			CA
		ZIP:			95035
		BUSINESS PHONE:		4089458600

	MAIL ADDRESS:	
		STREET 1:		691 SOUTH MILPITAS BLVD
		STREET 2:		M/S25
		CITY:			MILPITAS
		STATE:			CA
		ZIP:			95035

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KENNEDY JOSEPH S
		CENTRAL INDEX KEY:			0001246053

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-15071
		FILM NUMBER:		05731759

	BUSINESS ADDRESS:	
		STREET 1:		691 S MILPITAS BLVD
		CITY:			MILPITAS
		STATE:			CA
		ZIP:			95035
		BUSINESS PHONE:		4089458600
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-03-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000709804</issuerCik>
        <issuerName>ADAPTEC INC</issuerName>
        <issuerTradingSymbol>adpt</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001246053</rptOwnerCik>
            <rptOwnerName>KENNEDY JOSEPH S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>691 SOUTH MILPITAS BLVD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MILPITAS</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95035</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Non Qualified Stock Option</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>4.58</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-03-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>15000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2006-03-31</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2015-03-31</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>15000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>100000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">These options were granted pursuant to Adaptec, Inc.'s 2000 Director Stock Option Plan (the &quot;Plan&quot;). Pursuant to the Plan, each non-employee Director shall be automatically granted an option to purchase 15,000 shares of Adaptec, Inc. common stock on March 31st each year. These options become vested and exercisable as to 25% of the options at the end of each full quarter after the grant date. The option will have vested in full as of 3/31/2006.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>JOSEPH KENNEDY</signatureName>
        <signatureDate>2005-04-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----