Poly (DL-lactic acid-co-glycolic acid)-co-poly-(ethylene glycol) was synthesized by bulk ring-opening polymerization of DL-lactide/glycolide/poly(ethylene glycol) using stannous chloride as an initiator. The molecular structure of the copolymer was analyzed by IR, H-1 NMR, and DSC. The degradation behavior of copolymer was assayed by the reduction of molecular weight, the loss-in-mass, and the changes of pH value for degradation medium. The different contents of PGA and PEG in the molecules of the copolymer could control the degradation rate of polymer. Human Serum Albumin (HSA) was chosen as the model hydrophilic drug and encapsulated in the copolymer. The HA-loaded copolymer microspheres were characterized by the diameter, diameter distribution of the microspheres, and the loading efficiency. (C) 2003 Wiley Periodicals, Inc.