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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-08-09</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000108215</issuerCik>
        <issuerName>WOODHEAD INDUSTRIES INC</issuerName>
        <issuerTradingSymbol>WDHD</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001189271</rptOwnerCik>
            <rptOwnerName>NORTON SARILEE K</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3 PARKWAY NORTH, SUITE 550</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>DEERFIELD</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60015</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Woodhead Industries, Inc. Common Stock, $1 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2006-08-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>19.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Director Stock Option (right-to-buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>14.83</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-08-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2650</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.42</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2002-04-25</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2011-10-25</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, $1 Par Value</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2650</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Director Stock Option (right-to-buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>16.05</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-08-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1350</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.20</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2002-07-25</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2012-01-25</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, $1 Par Value</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1350</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Director Stock Option (right-to-buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>10.375</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-08-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>8.875</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2003-04-30</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2012-10-31</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, $1 Par Value</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Director Stock Option (right-to-buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>16.46</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-08-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>2.79</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2004-04-30</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2013-10-30</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, $1 Par Value</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Director Stock Option (right-to-buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>13.48</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-08-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.77</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2005-03-22</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2014-09-22</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, $1 Par Value</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents restricted stock that vested in connection with the Agreement and Plan of Merger dated as of June 30, 2006, by and between Molex, Inc., MLX Acquisition Corporation and Woodhead Industries, Inc. (the &quot;Merger Agreement&quot;). Such shares were disposed of for a cash payment of $19.25 per share, pursuant to the Merger Agreement.</footnote>
        <footnote id="F2">This option was canceled in the merger in exchange for a cash payment representing the difference between the exercise price of the option and the tender offer price of $19.25 per share, as set forth in the Merger Agreement.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Robert J. Tortorello for Sarilee K. Norton by Power of Attorney previously filed.</signatureName>
        <signatureDate>2006-08-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-08-09
1
0000108215
WOODHEAD INDUSTRIES INC
WDHD
0001189271
NORTON SARILEE K
3 PARKWAY NORTH, SUITE 550
DEERFIELD
IL
60015
1
0
0
0
Woodhead Industries, Inc. Common Stock, $1 Par Value
2006-08-09
4
D
0
2000
19.25
D
0
D
Director Stock Option (right-to-buy)
14.83
2006-08-09
4
D
0
2650
4.42
D
2002-04-25
2011-10-25
Common Stock, $1 Par Value
2650
0
D
Director Stock Option (right-to-buy)
16.05
2006-08-09
4
D
0
1350
3.20
D
2002-07-25
2012-01-25
Common Stock, $1 Par Value
1350
0
D
Director Stock Option (right-to-buy)
10.375
2006-08-09
4
D
0
4000
8.875
D
2003-04-30
2012-10-31
Common Stock, $1 Par Value
4000
0
D
Director Stock Option (right-to-buy)
16.46
2006-08-09
4
D
0
4000
2.79
D
2004-04-30
2013-10-30
Common Stock, $1 Par Value
4000
0
D
Director Stock Option (right-to-buy)
13.48
2006-08-09
4
D
0
4000
5.77
D
2005-03-22
2014-09-22
Common Stock, $1 Par Value
4000
0
D
Represents restricted stock that vested in connection with the Agreement and Plan of Merger dated as of June 30, 2006, by and between Molex, Inc., MLX Acquisition Corporation and Woodhead Industries, Inc. (the "Merger Agreement"). Such shares were disposed of for a cash payment of $19.25 per share, pursuant to the Merger Agreement.
This option was canceled in the merger in exchange for a cash payment representing the difference between the exercise price of the option and the tender offer price of $19.25 per share, as set forth in the Merger Agreement.
/s/ Robert J. Tortorello for Sarilee K. Norton by Power of Attorney previously filed.
2006-08-10