-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 CKph+5Vbzath3EQ2d49sCvCFlsb6ir4Q4ZQuJiYJPx4O5vxRMdTupRNS+UULZRpN
 KUCjgvviybfTrlk5cp8ZjQ==

<SEC-DOCUMENT>0000352541-08-000049.txt : 20080618
<SEC-HEADER>0000352541-08-000049.hdr.sgml : 20080618
<ACCEPTANCE-DATETIME>20080618123630
ACCESSION NUMBER:		0000352541-08-000049
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20080616
FILED AS OF DATE:		20080618
DATE AS OF CHANGE:		20080618

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ALLIANT ENERGY CORP
		CENTRAL INDEX KEY:			0000352541
		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTRIC & OTHER SERVICES COMBINED [4931]
		IRS NUMBER:				391380265
		STATE OF INCORPORATION:			WI
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		4902 NORTH BILTMORE LANE
		STREET 2:		PO BOX 77007
		CITY:			MADISON
		STATE:			WI
		ZIP:			53707-1007
		BUSINESS PHONE:		608-458-3314

	MAIL ADDRESS:	
		STREET 1:		4902 NORTH BILTMORE LANE
		STREET 2:		PO BOX 77007
		CITY:			MADISON
		STATE:			WI
		ZIP:			53707-1007

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	INTERSTATE ENERGY CORP
		DATE OF NAME CHANGE:	19980427

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	WPL HOLDINGS INC
		DATE OF NAME CHANGE:	19920703

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			MCALLISTER SINGLETON B
		CENTRAL INDEX KEY:			0001209079

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-09894
		FILM NUMBER:		08905143

	MAIL ADDRESS:	
		STREET 1:		427 WALKER ROAD
		CITY:			GREAT FALLS
		STATE:			VA
		ZIP:			22066
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-06-16</periodOfReport>

    <issuer>
        <issuerCik>0000352541</issuerCik>
        <issuerName>ALLIANT ENERGY CORP</issuerName>
        <issuerTradingSymbol>LNT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001209079</rptOwnerCik>
            <rptOwnerName>MCALLISTER SINGLETON B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>PO BOX 14720</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MADISON</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>53708-0720</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-06-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>827.533</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>36.7357</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4731.716</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>F. J. Buri</signatureName>
        <signatureDate>2008-06-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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