Block copolymers consisting of poly(L-lactide) (PLLA) and poly(oxyethylene-co-oxypropylene), with various compositions, were synthesized and characterized in vitro and in vivo for their application as postoperative adhesion prevention membranes. It was found that the flexibility and degradability of the cast films of the block copolymers grew with increasing Pluronic F68 [PN; poly(oxyethylene-co-oxypropylene] composition. The receding contact angle of the copolymer films against water became lower than that of the PLLA film, because the surface was predominantly covered with more hydrophilic PN segments in a wet state. This surface property significantly affects the cell attachment property of the copolymer films, and the fibroblasts cultured on the films exhibit a spheroid-like morphology. The copolymer films subcutaneously implanted in the back of rats induced milder tissue responses compared with PLLA homopolymers, because of the increased surface hydrophilicity in the former. In vivo evaluation using a uterus horn model in rats revealed that the performance of these copolymer films as an adhesion-prevention membrane is comparable to that of a conventionally utilized membrane of oxidized regenerated cellulose. These results indicate that the copolymer films are biocompatible materials with controllable mechanical properties and biodegradability as adhesion-prevention membranes.