The invention discloses a coordination compound comprising (1,2-diaminocyclohexane)platinum (II) moiety and poly(ethylene glycol)-block-poly(glutamic acid) copolymer moiety and its use as an anti-cancer agent. The characteristic feature lies in the use of a copolymer whose poly(glutamic acid) segment has a chain length consisting of, on an average, less than 35 repeating units.