The present invention relates to immunoglobulin Fc variants having an increased binding affinity for FcRn, which is characterized by including one or more amino acid m odifications selected from the group consisting of 307S, 308F, 380S, 380A, 428L, 429K, 430S, 433K and 434S (this numbering is according to the EU index) in the constant r egion of a native immunoglobulin Fc fragment. Owing to the high binding affinity for F cRn, the immunoglobulin Fc variants according to the present invention show more prol onged in vivo half-life, and thus can be used for the preparation of a long-acting formul ation of protein drugs.
