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

    <schemaVersion>X0306</schemaVersion>

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    <periodOfReport>2016-06-21</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001344413</issuerCik>
        <issuerName>Alexza Pharmaceuticals Inc.</issuerName>
        <issuerTradingSymbol>ALXA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001612008</rptOwnerCik>
            <rptOwnerName>Kamemoto Edwin S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ALEXZA PHARMACEUTICALS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>2091 STIERLIN COURT</rptOwnerStreet2>
            <rptOwnerCity>MOUNTAIN VIEW</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94043</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP, R&amp;D, Regulatory &amp; Quality</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

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            </transactionTimeliness>
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                    <footnoteId id="F1"/>
                </transactionShares>
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            <exerciseDate>
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            <expirationDate>
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            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
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                <transactionCode>D</transactionCode>
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            <transactionTimeliness>
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                <transactionPricePerShare>
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            <exerciseDate>
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            <expirationDate>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
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        <derivativeTransaction>
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            <conversionOrExercisePrice>
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            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-06-21</value>
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            <deemedExecutionDate></deemedExecutionDate>
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            <transactionTimeliness>
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            <transactionAmounts>
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                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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            <exerciseDate>
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            <expirationDate>
                <value>2024-05-20</value>
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            <transactionDate>
                <value>2016-06-21</value>
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            <deemedExecutionDate></deemedExecutionDate>
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                <equitySwapInvolved>0</equitySwapInvolved>
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                <value></value>
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            <transactionAmounts>
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                    <footnoteId id="F3"/>
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                <transactionPricePerShare>
                    <value>0.00</value>
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                <transactionAcquiredDisposedCode>
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            <exerciseDate>
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            <securityTitle>
                <value>Stock Option (right to buy)</value>
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            <transactionDate>
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            <exerciseDate>
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    </derivativeTable>

    <footnotes>
        <footnote id="F1">Includes 6,250 previously reported shares issued as restricted stock units (&quot;RSUs&quot;) under the Issuer's 2005 Equity Incentive Plan (the &quot;Plan&quot;). Per Section 3.4(b) of the Agreement and Plan of Merger, dated 5/9/16, among the Issuer, Grupo Ferrer Internactional, S.A. and Ferrer Pharma Inc. (the &quot;Agreement), each RSU outstanding immediately prior to the Offer Closing (as defined in the Agreement) became fully vested immediately prior to the Offer Closing.</footnote>
        <footnote id="F2">Per the terms of the Agreement and the Offer (as defined in the Agreement), each share of the Issuer's common stock was tendered for $0.90 per share in cash, without interest and less any required withholding taxes, plus one contractual contingent value right per share (&quot;CVR&quot;) (as defined in the Agreement).</footnote>
        <footnote id="F3">Disposed of per Section 3.4(a) of the Agreement, whereby each option that was outstanding immediately prior to the Offer Closing (as defined in the Agreement) was cancelled without consideration.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Brent D. Fassett, as Attorney-in-Fact for Edwin S. Kamemoto</signatureName>
        <signatureDate>2016-06-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
