A novel coordination-responsive block copolymer composed of polyether and polyester with selenium at the center was designed and synthesized for controlled drug delivery. The aqueous system of the new copolymer was a free-flowing solution at ambient temperature and turned into a semi-solid thermogel at body temperature. We demonstrate that the selenium-containing copolymer is capable of coordinating with the antitumor drug cisplatin. The efficient coordination between them significantly increased the loading capacity of cisplatin in the selenium-containing thermogel matrix, and the presence of glutathione in the release medium triggered the cisplatin release by coordination competition in a sustained release manner.