Abstract: Poly(lactic-co-glycolic acid)(PLGA)microparticles were prepared by an emulsion-solvent evaporation technique using bovine serum albumin(BSA)as model drug. When the ratio of shell to core was 1:1, ratio of water to oil 3:5, dispersant concentration 0.5%, and the ultrasonic emulsification time 2 min, PLGA microparticles were 268.7 nm in diameter, characterized by the laser light scattering technique, and the drug content and drug encapsulation efficiency in this case were 30.88% and 46.95%, respectively. Scanning electron microscopy(SEM)and transmission electron microscope(TEM)showed the products were spherical in shape and uniform in dimension. When the PLGA microparticles surface was modified with chitosan(CS)by adsorption technique, the microparticle became larger in diameter. The presence of N element and the positive zeta potential of modified microparticles revealed the presence of CS on the surface of the PLGA microparticles. In vitro drug release test showed that the burst release of modified microparticles eased and the release time was prolonged compared with unmodified PLGA microparticles.