Poly(5-benzyloxy-trimethylene carbonate-co-glycolide) random copolymers were synthesized through the ring-opening polymerization of 5-benzyloxy-trimethylene carbonate and glycolide (GA). The copolymers with different compositions, PBG-1 with 17% GA units and PBG-2 with 45% GA units, were obtained. Using these copolymers, microsphere drug delivery systems with submicron sizes were fabricated using an "ultrasonic assisted precipitation method." The in-vitro drug release from these microspheres was investigated. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 3451-3455, 2010