An objective of the present invention is to provide a polypeptide containing an Fc region having maintained or decreased binding activities towards both allotypes of Fc³RIIa, types H and R, and having enhanced Fc³RIIb-binding activity in comparison with a parent polypeptide； a pharmaceutical composition containing the polypeptide； an agent for treating or preventing immunological inflammatory diseases that includes the pharmaceutical composition； a production method thereof； and a method for maintaining or decreasing binding activities towards both allotypes of Fc³RIIa and enhancing the Fc³RIIb-binding activity. Specifically, it is found that a polypeptide containing an antibody Fc region that has an alteration of substituting Pro at position 238 (EU numbering) with Asp or Leu at position 328 (EU numbering) with Glu enhances Fc³RIIb-binding activity, and maintains or decreases binding activities towards both allotypes of Fc³RIIa, types H and R. It is also found that a polypeptide containing an antibody Fc region that contains an alteration of substituting Pro at position 238 (EU numbering) with Asp and several other alterations, enhances Fc³RIIb-binding activity, and maintains or decreases binding activities towards both allotypes of Fc³RIIa, types H and R.
