Recently, many antitumor agents developed. Irinotecan hycrochloride (CPT) has a great side effect even though it is well effective against the cancer. Drug delivery system (DDS) medicine indicates that the release rate of medicine is constant for a long time. Therefore, in order to materialize the general idea of DDS, we applied microencapsulation technique to prepare biodegradable polymer microspheres (MS) enclosing antitumor drug having no side effect. Polylactide microparticles enclosing antitumor agent were prepared by solvent evaporation method under various operation conditions. The effects of operation parameter on release rate of drug and morphology of microparticles were studied.