The PLA-CEZ microspheres were prepared successfully by the double emulsion method and were characterized by scanning electron microscope(SEM),differential thermal analysis(DTA) and IR spectroscopy.The results demonstrated that the PLA-CEZ microspheres were spherical and polylactic acid mingled together with cefazolin sodium.The effects of molecular weight of PLA and medium on the drug-releasing performance of the PLA microspheres were also investigated.