Disclosed is a polymer conjugate of folic acid or a folic acid derivative, wherein an amide bond is not used. The compound has chemical stability and adequate drug release rate in the living organism. Specifically disclosed is a polymer conjugate of folic acid or a folic acid derivative, wherein a substituent represented by formula (I) is bonded to a carboxy group of a block copolymer which is composed of a polyethylene glycol and a polymer having a carboxy group in a side chain, or a pharmacologically acceptable salt thereof. [In the formula, A represents a monocyclic or fused aromatic group; G represents an optionally substituted (C1-C6) alkylene group; Y represents a hydrogen atom or a substituent; and E represents a residue of folic acid or a folic acid derivative.]