A low molecular weight polymer-conjugated platinum complex with potential antineoplastic activity. This polymer drug delivery system consists of cytotoxic diaminocyclohexane (DACH)-platinum (Pt) coupled to a water-soluble biocompatible hydroxypropylmethacrylamide (HPMA) copolymer via a pH sensitive linker. Due to decreased pH in tumor sites, the linker is cleaved and the chelated active moiety DACH-Pt is released in tumor cells. DACH-Pt alkylates macromolecules and causes both inter- and intra-strand platinum-DNA crosslinks, which impede DNA replication and transcription, resulting in cell-cycle independent cytotoxicity. The HPMA-based drug delivery system increases the concentration and prolongs the half-life of DACH-Pt in tumor sites, while minimizing adverse effects on normal tissues.