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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2005-01-12</periodOfReport>

    <dateOfOriginalSubmission>2005-01-25</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000054681</issuerCik>
        <issuerName>KATY INDUSTRIES INC</issuerName>
        <issuerTradingSymbol>KT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001192892</rptOwnerCik>
            <rptOwnerName>CARROLL AMELIA M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>7505 VILLAGE SQUARE DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 200</rptOwnerStreet2>
            <rptOwnerCity>CASTLE ROCK, CO</rptOwnerCity>
            <rptOwnerState>X1</rptOwnerState>
            <rptOwnerZipCode>80108</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8729</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4212</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Note 3</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>804635</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F4"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Notes 1 and 4</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2071036</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F5"/>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Notes</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F5"/>
                    <footnoteId id="F6"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2005-01-12</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2005-01-12</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>G</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>12400</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>169839</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Spouse</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Options to purchase common stock</value>
                <footnoteId id="F7"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>5.91</value>
                <footnoteId id="F7"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2004-05-27</value>
                <footnoteId id="F7"/>
            </exerciseDate>
            <expirationDate>
                <value>2014-05-27</value>
                <footnoteId id="F7"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>27000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>27000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F7"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By spouse</value>
                    <footnoteId id="F7"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Members of the Reporting Person's immediate family are beneficiaries of the Wallace E. and Lelia H. Carroll Trust U/A Dated 5/1/58 F/B/O Wallace E. Carroll, Jr. and his descendants (the &quot;WEC Jr. '58 Trust&quot;), the Lelia H. Carroll Trust U/A Dated 7/12/62 F/B/O Wallace E. Carroll, Jr. (the &quot;WEC Jr. '62 Trust) and the Family Grandchildren Trust U/A dated 9/29/90 F/B/O the descendents of Wallace E. Carroll, Jr. (the ?Family Trust?) (collectively, the ?WEC Trusts?).

The WEC Jr. '58 Trust, the WEC Jr. '62 Trust and the Family Trust directly beneficially own 603,000, 194,693 and 6,942 shares of the Issuer's outstanding common stock, respectively, for an aggregate of 804,635 shares (the ?Trust Shares?).  The Reporting Person may be deemed to have an indirect pecuniary interest in the Trust Shares to the extent that she and/or the members of her immediate family living in the same household are beneficiaries of the WEC Trusts.</footnote>
        <footnote id="F2">CRL, Inc. (&quot;CRL&quot;) directly beneficially owns 2,071,036 shares of the Issuer's outstanding common stock (the ?CRL Shares?) after giving effect to the transaction reported herein.  As stockholders of CRL, the WEC Jr. '58 Trust and the Reporting Person may be deemed to indirectly beneficially own such Shares.  The Reporting Person may be deemed to have an indirect pecuniary interest in the shares indirectly beneficially owned by the WEC Jr. '58 Trust through CRL to the extent that he and/or the members of his immediate family living in the same household are beneficiaries of that trust and as a stockholder of CRL.</footnote>
        <footnote id="F3">Common stock is held by the Katy Industries, Inc. Directors? Deferred Compensation Plan in a Rabbi Trust arrangement.  2,106 shares are held for the benefit of the Reporting Person, and 2,106 shares are held for the benefit of her spouse.</footnote>
        <footnote id="F4">Members of the Reporting Person?s immediate family are beneficiaries of the WEC Trusts (see Note 1).  The Reporting Person may be deemed to have an indirect pecuniary interest in the Trust Shares to the extent that members of her immediate family living in the same household are beneficiaries of the WEC Trusts.</footnote>
        <footnote id="F5">The Reporting Person may be deemed to have an indirect pecuniary interest in the CRL Shares to the extent that members of her immediate family living in the same household own CRL shares and are beneficiaries of the WEC Jr. '58 Trust (see Note 2).</footnote>
        <footnote id="F6">As a stockholder of CRL, the Reporting Person may be deemed to have an indirect pecuniary interest in the CRL Shares (see Note 2).</footnote>
        <footnote id="F7">The Reporting Person's spouse has received stock options from 1995 through 2004.  The execution date, expiration date and conversion price represent the most recent stock option grant.  Range of conversion prices are from $3.11 - $18.125.</footnote>
    </footnotes>

    <remarks>Gift of 12,400 shares from Amelia's husband, Wallace E. Carroll, Jr., to their grandchildren.</remarks>

    <ownerSignature>
        <signatureName>/s/ Michael Paul, as attorney-in-fact for Amelia M. Carroll</signatureName>
        <signatureDate>2005-06-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
