A polymer conjugate of a physiologically active substance, which enables drug release independent of a biological enzyme and can be expected to have a high therapeutic effect, is demanded.Provided is a polymer conjugate of a physiologically active substance, comprising a block copolymer of a polyethylene glycol moiety and a polymer having two or more carboxy groups, in which a substituent represented by general formula (I) or general formula (II) is linked to at least one of the side-chain carboxy groups of the block copolymer via an amide bond [in the formula, R8 and R9 each independently are hydrogen atom or (C1-C6)alkyl which may have a substituent, R10 is hydrogen atom, (C1-C40)alkyl which may have a substituent, (C1-C40) aralkyl group which may have a substituent, an aromatic group which may have a substituent, an amino acid residue having a protected carboxy group, or a sugar residue which may have a substituent, CX—CY represents CH—CH or C═C (double bond), and A represents a residue obtained by removing, from a physiologically active substance having one or more hydroxy groups, one of the one or more hydroxy groups].