PROBLEM TO BE SOLVED: To provide an Fc variant having a mutated binding to FcRn. The application relates to a mutant Fc region comprising at least one modification relative to a wild type human Fc region, wherein the modification is selected from the group consisting of 434S, 252Y/428L, 252Y/434S, and 428L/434S. The numbering depends on the EU index. [Selection diagram] None【課題】FcRnへの変異結合を有するFc変異体の提供。【解決手段】本出願は、野生型ヒトFc領域と比べて少なくとも1つの修飾を含む変異Fc領域に関し、該修飾は、434S、252Y/428L、252Y/434S、および428L/434Sから成る群から選択され、付番はEUインデックスによる。【選択図】なし