The present invention addresses the problem of acquiring a preparation which can be highly accumulated in an affected part and the blood concentration of which can be maintained at a constant level without varying from person to person so that the efficacy and safety thereof are remarkably improved and dose control depending on the kinetics in blood (trough concentration in blood) thereof becomes unnecessary. The present invention pertains to a polymeric derivative of tacrolimus characterized in that an alcoholic hydroxyl group of tacrolimus is attached to a carboxy group in a side chain of a copolymer, said copolymer comprising a polyethylene glycol segment and a polymer moiety having a carboxy group in a side chain.本案發明之課題在於獲得一種製劑，其藉由對患部表現出較高之聚集性、且無個人差異地維持一定之血中濃度，從而有效性與安全性顯著提高，無需根據血中動態(血中最低藥物濃度)而控制投予量。本案發明係關於一種他克莫司之高分子衍生物，其特徵在於：於包含聚乙二醇鏈段及側鏈具有羧基之聚合物部分的共聚物之側鏈之羧基上鍵結有他克莫司之醇性羥基。
