The present inventors succeeded in improving the antibody constant region to have increased stability under acid conditions, reduced heterogeneity originated from disulfide bonds in the hinge region, reduced heterogeneity originated from the H chain C terminus, and increased stability at high concentrations as well as in discovering novel constant region sequences having reduced Fcγ receptor-binding, while minimizing the generation of novel T-cell epitope peptides. As a result, the present inventors successfully discovered antibody constant regions with improved physicochemical properties (stability and homogeneity), immunogenicity, safety, and pharmacokinetics.