Disclosed is a water-soluble high-molecular weight conjugate of physiologically active substances which enable medicament to release without depending on the enzymes in a living body and which is expected to have a useful therapeutic effect. A high-molecular weight conjugate of a physiologically active substance has a substituent group represented by a general formula (1) bonded to a side-chain carboxy group of a block copolymer which has a polyethylene glycol moiety and either a polyaspartic acid moiety or a polyglutamic acid moiety. Formula (1): -Ar-CR15R16-O-C(=O)-A [In the formula: Ar represents an aromatic hydrocarbon group optionally a substituent group, or an aromatic heterocyclic group optionally having a substituent group R15 and R16 independently represent a hydrogen atom or a (C1-C6) alkyl group optionally having a substituent group and A represents a residual group of a physiologically active substance that has an carboxy group, or a residual group of a physiologically active substance that has an amino group].
