Polypeptides with improved stability as compared to that of a parent polypeptide were successfully obtained by modifying at least one amino acid in a loop region of the antibody Fc region. Furthermore, by combining multiple amino acid modifications in the loop region, polypeptides with maintained or enhanced Fc³R-binding activity as well as improved thermal stability, polypeptides with decreased Fc³R-binding activity as well as improved thermal stability, and polypeptides with not only improved thermal stability and adjusted Fc³R-binding activity but also decreased aggregate content, as compared to those of a parent polypeptide, were successfully obtained.
