The present invention addresses the problem of obtaining a preparation which has improved efficacy and improved safety compared with tacrolimus and the blood level of which can be maintained constant without individual differences so that no dosing control based on kinetics in blood (blood trough concentration) thereof is required. The present invention relates to a polymer derivative of tacrolimus wherein a polyethylene glycol segment and an alcoholic hydroxyl group of tacrolimus are bonded to a side-chain carboxy group of a polyaspartic acid derivative.本發明之課題在於獲得一種製劑，其與他克莫司相比有效性與安全性提高，血中濃度維持固定而無個體差異，藉此不需要根據血中動態(血中谷濃度)而控制投予量。 本發明係關於一種他克莫司之高分子衍生物，其係於聚天冬胺酸衍生物之側鏈羧基上鍵結有聚乙二醇鏈段及他克莫司之醇性羥基者。
