We developed the BSA loaded PLGA microspheres using a sodium alginate and water-in-oil-water (W/ O/W) solvent evaporation method for sustaining release of BSA and recognized the release behavior according to sodium alginate concentration. We characterized the surface and the cross-section morphology of prepared PLGA microspheres by the SEM and behavior of BSA release from microspheres for 45 days by BCA assay method. After 45 days, the molecular weight change of PLGA was measured by GPC. The surface of microspheres appeared sphere shape and had may pores. According to sodium alginate concentration increasing, the size of microspheres increased and release rate of BSA from microspheres decreased. These results show that the change of sodium alginate concentration can control the release behaviors.