[Problem]To provide a novel polymer derivative of a cytidine metabolic antagonist which allows release of a medicament irrespective of enzymes of the living body and is expected to have high therapeutic effects.[Solution]The polymer derivative of a cytidine metabolic antagonist in which a substituent represented by the general formula (I) or the general formula (II) [wherein R7 and R8 each independently represent a hydrogen atom or an optionally substituted (C1-C6)alkyl group, R6 represents a hydrogen atom, an optionally substituted (C1-C40)alkyl group, an optionally substituted (C1-C40)aralkyl group, an optionally substituted aromatic group, an amino acid residue in which the carboxy group is protected, or an optionally substituted sugar residue, CX-CY represents CH-CH or C=C (double bond), and A represents the residue of the cytidine metabolic antagonist except the amino group at the position 4] is bonded to the side-chain carboxy group of a block copolymer of a polyethylene-glycol structural moiety and a polymer having 10 or more carboxy groups.
