The present invention relates to a recombinant antibody composition having higher complement-dependent cytotoxic activity than a human IgG1 antibody and a human IgG3 antibody, wherein a polypeptide comprising a CH2 domain in the Fc region of a human IgG1 antibody is replaced by a polypeptide comprising an amino acid sequence which corresponds to the same position of a human IgG3 antibody indicated by the EU index as in Kabat, et al.; a DNA encoding the antibody molecule or a heavy chain constant region of the antibody molecule contained in the recombinant antibody composition; a transformant obtainable by introducing the recombinant vector into a host cell; a process for producing the recombinant antibody composition using the transformant; and a medicament comprising the recombinant antibody composition as an active ingredient.