Uniformly sized microspheres of poly(d, l-lactic-co-glycolic) (PLGA) encapsulating tamoxifen(TAM) were successfully prepared by solvent evaporation. In this study three different polylactide-co-glycolides were used with differing lactide-glycolide ratios (50:50, 75:25, and 85:15, respectively). The sphere size distribution and morphology was analyzed using Laser Particle Size Analyzer and SEM. The drug loading and release in vitro of the microspheres were also investigated. The result showed that the microspheres have good spherical and better sustained release.