<ownershipDocument><schemaVersion>X0201</schemaVersion>    <documentType>4</documentType><periodOfReport>2004-01-02</periodOfReport><notSubjectToSection16>0</notSubjectToSection16><issuer><issuerCik>0000783325</issuerCik><issuerName>WISCONSIN ENERGY CORP</issuerName>        <issuerTradingSymbol>WEC</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId><rptOwnerCik>0001017659</rptOwnerCik><rptOwnerName>ABDOO RICHARD A</rptOwnerName></reportingOwnerId><reportingOwnerAddress><rptOwnerStreet1>231 WEST MICHIGAN STREET</rptOwnerStreet1><rptOwnerStreet2></rptOwnerStreet2><rptOwnerCity>MILWAUKEE</rptOwnerCity><rptOwnerState>WI</rptOwnerState><rptOwnerZipCode>53203</rptOwnerZipCode><rptOwnerStateDescription></rptOwnerStateDescription></reportingOwnerAddress><reportingOwnerRelationship><isDirector>1</isDirector><isOfficer>1</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther><officerTitle>CEO &amp; Chairman</officerTitle><otherText></otherText></reportingOwnerRelationship></reportingOwner><nonDerivativeTable><nonDerivativeHolding><securityTitle><value>Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>67080</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></nonDerivativeHolding><nonDerivativeHolding><securityTitle><value>Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>11120</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Spouse</value></natureOfOwnership></ownershipNature></nonDerivativeHolding><nonDerivativeHolding><securityTitle><value>Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>17736</value><footnoteId id="F2"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>ERSP</value></natureOfOwnership></ownershipNature></nonDerivativeHolding></nonDerivativeTable><derivativeTable><derivativeTransaction><securityTitle><value>Stock Options (Right to buy)</value></securityTitle><conversionOrExercisePrice><value>33.435</value></conversionOrExercisePrice><transactionDate><value>2004-01-02</value></transactionDate><deemedExecutionDate></deemedExecutionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>2990</value></transactionShares><transactionPricePerShare><value>0</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2005-01-02</value><footnoteId id="F3"/></exerciseDate><expirationDate><value>2014-01-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>2990</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>2990</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeTransaction><derivativeTransaction><securityTitle><value>Stock Options (Right to buy)</value></securityTitle><conversionOrExercisePrice><value>33.435</value></conversionOrExercisePrice><transactionDate><value>2004-01-02</value></transactionDate><deemedExecutionDate></deemedExecutionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>297010</value></transactionShares><transactionPricePerShare><value>0</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2005-01-02</value><footnoteId id="F4"/></exerciseDate><expirationDate><value>2014-01-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>297010</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>300000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeTransaction></derivativeTable><footnotes><footnote id="F1">Includes shares acquired pursuant to a dividend  reinvestment feature of WEC's Stock Plus Investment Plan in transactions exempt from Section 16 pursuant to Rule 16a-11.</footnote><footnote id="F2">Includes shares acquired under WEC's Employee Retirement Savings Plan (ERSP) in transactions exempt from Section 16(b) pursuant to Rule 16b-3(c) and exempt from reporting pursuant to Rule 16a-3(f)(1)(i)(B).  The number of shares in the ERSP attributable to any one particpant varies with the price of the Common Stock.  The information in this report is based on a plan statement dated as of January 2, 2004.</footnote><footnote id="F3">The reporting person has not engaged in any transaction in the WEC Executive Deferred Compensation Plan (EDCP).  However, the reported holdings as of the date indicated include shares acquired pursuant to a dividend  reinvestment feature of the plan which are exempt from Section 16 pursuant to Rule 16a-11.</footnote><footnote id="F4">Options vest in 25% increments annually beginning on the date indicated.</footnote></footnotes><ownerSignature><signatureName>Kristine A. Rappe as Attorney-in-Fact</signatureName><signatureDate>2004-01-06</signatureDate></ownerSignature></ownershipDocument>
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X0201
4
2004-01-02
0
0000783325
WISCONSIN ENERGY CORP
WEC
0001017659
ABDOO RICHARD A
231 WEST MICHIGAN STREET
MILWAUKEE
WI
53203
1
1
0
0
CEO & Chairman
Common Stock
67080
D
Common Stock
11120
I
By Spouse
Common Stock
17736
I
ERSP
Stock Options (Right to buy)
33.435
2004-01-02
4
A
0
2990
0
A
2005-01-02
2014-01-02
Common Stock
2990
2990
D
Stock Options (Right to buy)
33.435
2004-01-02
4
A
0
297010
0
A
2005-01-02
2014-01-02
Common Stock
297010
300000
D
Includes shares acquired pursuant to a dividend  reinvestment feature of WEC's Stock Plus Investment Plan in transactions exempt from Section 16 pursuant to Rule 16a-11.
Includes shares acquired under WEC's Employee Retirement Savings Plan (ERSP) in transactions exempt from Section 16(b) pursuant to Rule 16b-3(c) and exempt from reporting pursuant to Rule 16a-3(f)(1)(i)(B).  The number of shares in the ERSP attributable to any one particpant varies with the price of the Common Stock.  The information in this report is based on a plan statement dated as of January 2, 2004.
The reporting person has not engaged in any transaction in the WEC Executive Deferred Compensation Plan (EDCP).  However, the reported holdings as of the date indicated include shares acquired pursuant to a dividend  reinvestment feature of the plan which are exempt from Section 16 pursuant to Rule 16a-11.
Options vest in 25% increments annually beginning on the date indicated.
Kristine A. Rappe as Attorney-in-Fact
2004-01-06