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

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    <documentType>4</documentType>

    <periodOfReport>2021-07-28</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001739410</issuerCik>
        <issuerName>Rallybio Corp</issuerName>
        <issuerTradingSymbol>RLYB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001872879</rptOwnerCik>
            <rptOwnerName>Fryer Jeffrey M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O RALLYBIO CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>234 CHURCH STREET, SUITE 1020</rptOwnerStreet2>
            <rptOwnerCity>NEW HAVEN</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06510</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>See Remarks</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

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                <natureOfOwnership>
                    <value>See Footnote</value>
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        <nonDerivativeTransaction>
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                <natureOfOwnership>
                    <value>See Footnote</value>
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                <natureOfOwnership>
                    <value>See Footnote</value>
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                <natureOfOwnership>
                    <value>See Footnote</value>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
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                <natureOfOwnership>
                    <value>See Footnote</value>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
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                <value></value>
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            <transactionAmounts>
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                <transactionPricePerShare>
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                    <footnoteId id="F7"/>
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                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
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    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
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                <transactionPricePerShare>
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            <expirationDate>
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            <ownershipNature>
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                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F3"/>
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        <derivativeTransaction>
            <securityTitle>
                <value>Common  Units</value>
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            <transactionTimeliness>
                <value></value>
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            <transactionAmounts>
                <transactionShares>
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                <transactionPricePerShare>
                    <footnoteId id="F1"/>
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            <expirationDate>
                <footnoteId id="F1"/>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
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                <underlyingSecurityShares>
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                <sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
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                <natureOfOwnership>
                    <value>See footnote</value>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            </transactionAmounts>
            <exerciseDate>
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            <expirationDate>
                <footnoteId id="F1"/>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
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                <underlyingSecurityShares>
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                </underlyingSecurityShares>
            </underlyingSecurity>
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            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F5"/>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Series A-1 Preferred Units</value>
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            <transactionDate>
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                <footnoteId id="F1"/>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
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                <transactionAcquiredDisposedCode>
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            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
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            <expirationDate>
                <footnoteId id="F1"/>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
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                </underlyingSecurityShares>
            </underlyingSecurity>
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                <sharesOwnedFollowingTransaction>
                    <value>0</value>
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            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
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        <derivativeTransaction>
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            <transactionTimeliness>
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                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
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                <transactionAcquiredDisposedCode>
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            <expirationDate>
                <footnoteId id="F1"/>
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            <underlyingSecurity>
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                </underlyingSecurityShares>
            </underlyingSecurity>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F5"/>
                </natureOfOwnership>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Series A-2 Preferred Units</value>
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            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
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            <transactionDate>
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            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
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            <transactionAmounts>
                <transactionShares>
                    <value>100000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
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                <transactionAcquiredDisposedCode>
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            <exerciseDate>
                <footnoteId id="F1"/>
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            <expirationDate>
                <footnoteId id="F1"/>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
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                <underlyingSecurityShares>
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            <ownershipNature>
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                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
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        <derivativeTransaction>
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            <transactionDate>
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                <footnoteId id="F1"/>
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            <transactionTimeliness>
                <value></value>
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            <transactionAmounts>
                <transactionShares>
                    <value>107891</value>
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                <transactionPricePerShare>
                    <footnoteId id="F1"/>
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                <transactionAcquiredDisposedCode>
                    <value>D</value>
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            <expirationDate>
                <footnoteId id="F1"/>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>13.00</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2021-07-28</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>160000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
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                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
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            <exerciseDate>
                <footnoteId id="F8"/>
            </exerciseDate>
            <expirationDate>
                <value>2031-07-28</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>160000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>160000</value>
                </sharesOwnedFollowingTransaction>
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                <directOrIndirectOwnership>
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        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The Common Units, Series A-1 Preferred Units, Series A-2 Preferred Units and Series B Preferred Units (collectively with the Series A-1 Preferred Units and Series A-2 Preferred Units, the &quot;Preferred Units&quot;) reported herein were units of Rallybio Holdings, LLC. The shares of common stock of the Issuer were received on July 28, 2021 pursuant to the Plan of Liquidation and Dissolution, dated July 28, 2021, among Rallybio Holdings, LLC and its members (the &quot;Plan of Liquidation&quot;). Pursuant to the Plan of Liquidation, the holders of Common Units, on an aggregate basis, received approximately 7.38 shares of common stock of the Issuer for each Common Unit and approximately 6.37 shares of common stock of the Issuer for each Preferred Unit. Rallybio Holdings, LLC was subsequently dissolved. The Common Units and Preferred Units had no expiration date prior to the liquidation.</footnote>
        <footnote id="F2">Shares of common stock are held in a Roth IRA.</footnote>
        <footnote id="F3">Shares of common stock are held in a revocable trust for which Mr. Fryer is the grantor.</footnote>
        <footnote id="F4">Shares of common stock are held in an irrevocable trust for the benefit of one of Mr. Fryer's children. Mr. Fryer disclaims beneficial ownership of such shares.</footnote>
        <footnote id="F5">Shares of common stock are held in an irrevocable trust for the benefit of one of Mr. Fryer's children. Mr. Fryer disclaims beneficial ownership of such shares.</footnote>
        <footnote id="F6">The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $8.01 to $9.00, inclusive. The reporting person undertakes to provide to Rallybio Corporation, any security holder of Rallybio Corporation, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set forth in footnotes (6) and (7) to this Form 4.</footnote>
        <footnote id="F7">The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $9.01 to $10.00, inclusive.</footnote>
        <footnote id="F8">The option vests as to 25% of the underlying shares of Common Stock on July 28, 2022 and as to the remaining 75% of the underlying shares of Common Stock in 36 equal monthly installments thereafter.</footnote>
    </footnotes>

    <remarks>Chief Financial Officer &amp; Treasurer</remarks>

    <ownerSignature>
        <signatureName>By: /s/ Michael Greco, Attorney-in-Fact</signatureName>
        <signatureDate>2022-01-11</signatureDate>
    </ownerSignature>
</ownershipDocument>
