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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-11-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000030302</issuerCik>
        <issuerName>ALCO STORES INC</issuerName>
        <issuerTradingSymbol>ALCS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001459132</rptOwnerCik>
            <rptOwnerName>Beaith Edmond C.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>401 COTTAGE STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ABILENE</rptOwnerCity>
            <rptOwnerState>KS</rptOwnerState>
            <rptOwnerZipCode>67410</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Sr. VP/CIO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-11-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>X</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>345</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>9.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>345</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock option (right to buy 08/25/2008)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>14.08</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2009-08-25</value>
                <footnoteId id="F2"/>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2013-08-25</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>10000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock option (right to buy 03/13/2009)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.25</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-11-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>X</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3750</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2010-03-13</value>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2014-03-13</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1250</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11250</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeHolding>
            <securityTitle>
                <value>Stock option (right to buy 04/30/2012)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.82</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2013-04-30</value>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <value>2017-04-30</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>7500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18750</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock option (right to buy 07/06/2012)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.43</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2013-07-06</value>
                <footnoteId id="F6"/>
            </exerciseDate>
            <expirationDate>
                <value>2022-07-06</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5250</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>24000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock option (performance based 07/06/2012)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.43</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F7"/>
            </exerciseDate>
            <expirationDate>
                <value>2022-07-06</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>12250</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>36250</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Shares were granted in exchange for the cancellation of Mr. Beaith's 3,750 vested stock options granted on March 13, 2009.  Mr. Beaith elected net exercise of his options so that in exchange for cancellation of his 3,750 vested options, he received the number of shares of ALCO, Inc.'s common stock equal to: the difference between $10.19, which is the fair market value of a share of ALCO, Inc.'s common stock on the exercise date of October 31, 2012 and the option price of $9.25, multiplied by 3,750, less any tax withholdings to the extent required, and divided by $10.19.</footnote>
        <footnote id="F2">The option becomes exercisable in four equal installments on August 25, 2009, 2010, 2011, and 2012.</footnote>
        <footnote id="F3">Mr. Beaith was not an Executive Officer when the August 25, 2008 stock option was granted therefore it was not reported at that time.</footnote>
        <footnote id="F4">The options become exercisable in four equal installments on March 13, 2010, 2011, 2012, and 2013.</footnote>
        <footnote id="F5">The options become exercisable in four equal installments on April 30, 2013, 2014, 2015, and 2016.</footnote>
        <footnote id="F6">The options become exercisable in four equal installments on July 6, 2013, 2014, 2015, and 2016.</footnote>
        <footnote id="F7">The options will one-half vest when Alco Stores, Inc. reaches a target Return on Equity of 5% as defined in the Company's Bonus Plan; and the remaining one-half will vest 12 months later if the optionee is still an employee of Alco Stores, Inc.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Edmond C. Beaith</signatureName>
        <signatureDate>2012-11-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
