PURPOSE: To obtain a conjugate biocompatible, biologically inert, highly stable in vivo and useful for augmentation of soft or hard tissues and so on by employing a conjugate comprising a specific compound, or a derivative thereof, chemically bonded to a hydrophilic synthetic polymer.

CONSTITUTION: A conjugate comprising a glycosaminoglycan or a derivative thereof is employed, where the glycosaminoglycan, preferably selected from the group consisting of hyaluronic acid, chondroitin sulfate A, chondroitin sulfate C, dermatan sulfate, heparin, keratan sulfate, kerato sulfate, chitin, chitosan 1, chitosan 2 and a derivative thereof, is chemically conjugated to a hydrophilic synthetic polymer, preferably a multifunctionally activated polyethylene glycol.