Poly-DL-lactide-poly(ethylene glycol) (PELA) block copolymer containing 10% of polyethylene glycol (PEG) wasprepared by bulk ring opening polymerization of lactide /PEG using stannous chloride as initiator. PELA microspherescontaining human serum albumin (HSA) were elaborated by solvent extraction method based on the formation of doublewlolw emulsion. In vitro matrix degradation characteristics of these microspheres were performed in phosphate-bufferedsaline at pH 5.6, 7.4 and 9.6. The degradation profiles were characterized by observing the morphological change ofmicrospheres and measuring the loss of microspheres mass, the decrease of polymer intrinsic viscosity, the decrease of pHvalue of degradation media, the reduction of polymer number-average molecular (M) and the change of polydispersity n (M/M). We determined that the degradation rate of the microspheres matrix in the media was as follows: pH 9.6.pH w n5.6.pH 7.4 during the initial 4 weeks and in the later incubation time the degradation rate was as follows: pH 5.6.pH7.4.pH 9.6. It was suggested that the pH of the degradation media had a big effect on the degradation rate of HSA/PELAmicrospheres matrix.