Abstract: Contraceptive poly ethylglycol- lactide (PEGL), an artificial biodegradable polymer microsphere was prepared by a solvent evaporation process using levonorgestrel (LNG) and estradiol (E₂) as model drugs and PEGL as the core material. The experimental conditions were optimized, the mean volume diameter obtained being 30 μm and rate of encapsulation 75～82%. In vitro, it was found that the drug release rate decreased with decreasing drug content in the microspheres. The microspheres of the contraceptive maintained anticonception duration in mice for over 6 months, indicating that the microspheres have remarkablely long acting sustained release action.