The present invention relates to a triblock copolymer, that is multipurpose yet has sufficient properties particularly for medical applications, and is useful as a material having excellent flexibility and water absorbability, as well as to a method for producing the same, and a biocompatible material. The copolymer of the present invention is composed of segments A.sup.1 and A.sup.2 each composed of a polymer having a depsipeptide unit, such as a segment selected from a homopolymer of depsipeptide or a copolymer of lactide and depsipeptide, and segment B composed of polyalkylene glycol, such as PEG, and is a A.sup.1-B-A.sup.2 triblock copolymer having a number average molecular weight of 8000 to 500000. The biocompatible material of the present invention contains the triblock copolymer as a main component, and may be used as a tissue anti-adhesion barrier.