PROBLEM TO BE SOLVED : To provide a protein comprising heterodimeric antibody Fc, pharmaceuticals comprising the same and methods for producing such a protein. SOLUTION : Disclosed herein is a heterodimeric protein comprising a first polypeptide comprising a first Fc region of an immunoglobulin, the first Fc region comprising a first CH3 region, and a second polypeptide comprising a second Fc region of an immunoglobulin, the second Fc region comprising a second CH3 region, where the sequences of the first and the second CH3 regions are different, and the heterodimeric interaction between the first and second CH3 regions is stronger than the interactions of homodimers each comprising the first or second CH regions, and the first homodimeric protein has an amino acid substitution in a specific amino acid sequence. SELECTED DRAWING : None COPYRIGHT : (C)2019, JPO&INPIT