-----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,
 Njs9tCQuPvGPlYiX/lZVrg4WaUXLnFNNwdvqrMQuRSDxB7y86FPvBev+klov0RUX
 Cco/x/rknivlCydwE9RoPA==

<SEC-DOCUMENT>0001161728-11-000007.txt : 20110302
<SEC-HEADER>0001161728-11-000007.hdr.sgml : 20110302
<ACCEPTANCE-DATETIME>20110302141523
ACCESSION NUMBER:		0001161728-11-000007
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20110301
FILED AS OF DATE:		20110302
DATE AS OF CHANGE:		20110302

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Possin James L
		CENTRAL INDEX KEY:			0001477220

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-49965
		FILM NUMBER:		11655548

	MAIL ADDRESS:	
		STREET 1:		133 SOUTH BLAIR STREET
		STREET 2:		P.O. BOX 1231
		CITY:			MADISON
		STATE:			WI
		ZIP:			53701-1231

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MGE ENERGY INC
		CENTRAL INDEX KEY:			0001161728
		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTRIC, GAS & SANITARY SERVICES [4900]
		IRS NUMBER:				392040501
		STATE OF INCORPORATION:			WI
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		133 SOUTH BLAIR STREET
		STREET 2:		P.O. BOX 1231
		CITY:			MADISON
		STATE:			WI
		ZIP:			53701-1231
		BUSINESS PHONE:		(608) 252-7000

	MAIL ADDRESS:	
		STREET 1:		133 SOUTH BLAIR STREET
		STREET 2:		P.O. BOX 1231
		CITY:			MADISON
		STATE:			WI
		ZIP:			53701-1231
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-03-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001161728</issuerCik>
        <issuerName>MGE ENERGY INC</issuerName>
        <issuerTradingSymbol>MGEE</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001477220</rptOwnerCik>
            <rptOwnerName>Possin James L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>133 SOUTH BLAIR STREET</rptOwnerStreet1>
            <rptOwnerStreet2>P.O. BOX 1231</rptOwnerStreet2>
            <rptOwnerCity>MADISON</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>53701-1231</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>MGEE Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-03-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>40.99</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>875</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>IRA</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Includes shares acquired through the reinvestment of dividends.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ James L. Possin</signatureName>
        <signatureDate>2011-03-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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