Abstract: Disclosed is a method for improving an affinity of an anti-cytokine antibody for an antigen, the method comprising: in an anti-cytokine antibody whose electrical characteristic of a complementarity determining region (CDR) is negatively charged, changing at least 3 amino acid residues of light chain framework region 3 to arginine residues or lysine residues, thereby improving an affinity for an antigen as compared with that of an antibody before the at least 3 amino acid residues are changed to arginine residues or lysine residues, wherein the at least 3 amino acid residues comprise residues at least 3 positions selected from the group consisting of positions 63, 65, 67, 70 and 72 of a light chain defined by Chothia method.