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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-02-13</periodOfReport>

    <issuer>
        <issuerCik>0000094049</issuerCik>
        <issuerName>STEPAN CO</issuerName>
        <issuerTradingSymbol>SCL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001244290</rptOwnerCik>
            <rptOwnerName>WEHMER EDWARD J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>22 W. FRONTAGE ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NORTHFIELD</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60093</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Directors Deferred Compensation Plan</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>31.70</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-02-13</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>473</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>31.70</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>1988-08-08</value>
            </exerciseDate>
            <expirationDate>
                <value>1988-08-08</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>473</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1059</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">On February 13, 2007, 473 shares were added to the Directors Deferred Compensation Plan account as per the provisions in the Stepan Company Directors Deferred Compensation Plan Amended and Restated as of January 1, 2005.  The 473 shares shall be paid to the director upon termination of service on the Board of Directors and shall be paid only in shares of Stepan Company Common Stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Kathleen M. Owens, by Power of Attorney for Edward J. Wehmer</signatureName>
        <signatureDate>2007-02-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2007-02-13
0000094049
STEPAN CO
SCL
0001244290
WEHMER EDWARD J
22 W. FRONTAGE ROAD
NORTHFIELD
IL
60093
1
0
0
0
Directors Deferred Compensation Plan
31.70
2007-02-13
4
J
0
473
31.70
A
1988-08-08
1988-08-08
Common Stock
473
1059
D
On February 13, 2007, 473 shares were added to the Directors Deferred Compensation Plan account as per the provisions in the Stepan Company Directors Deferred Compensation Plan Amended and Restated as of January 1, 2005.  The 473 shares shall be paid to the director upon termination of service on the Board of Directors and shall be paid only in shares of Stepan Company Common Stock.
Kathleen M. Owens, by Power of Attorney for Edward J. Wehmer
2007-02-15