A drug delivery system (DDS) preparation of a platinum complex which selectively releases a highly active platinum complex in cells in reductive conditions, and exhibits the required high antitumour activity as a drug is yet to be obtained, and thus a novel DDS preparation of a platinum complex which can be used clinically is in demand. Accordingly, a polymer conjugate of a hexa-coordinated platinum complex is provided in which the hexa-coordinated platinum complex, which has halogens and hydroxyl groups at axial positions, is bonded directly or via spacers to side-chain carboxyl groups of a block copolymer having a polyethylene glycol structure moiety and a polyaspartic acid moiety or a polyglutamic acid moiety.於還原條件之細胞內選擇性地釋出高活性之鉑錯合物而顯示出作為醫藥而被要求之高抗腫瘤活性的鉑錯合物之DDS製劑迄今尚未獲得，而期待臨床上可使用之新穎之鉑錯合物之DDS製劑。 本發明提供一種使於軸向位具有鹵素原子及羥基之6配位鉑錯合物直接或經由間隔基結合於具有聚乙二醇結構部分與聚天冬胺酸部分或聚麩胺酸部分之嵌段共聚物中之側鏈羧基而成的6配位鉑錯合物之高分子結合體。
