Poly(D

L-lactide-

co

-glycolide) (PLGA) microspheres were prepared by emulsion solvent evaporation method. The influences of inner aqueous phase

organic solvent

PLGA concentration on the morphology of microspheres were studied. The results showed that addition of porogen or surfactants to the inner aqueous phase

types of organic solvents and polymer concentration affected greatly the microsphere morphology. When dichloromethane was adopted as organic solvent

microspheres with porous structure were produced. When ethyl acetate served as organic solvent

two different morphologies were obtained. One was hollow microspheres with thin porous shell under a lower PLGA concentration

another was erythrocyte-like microspheres under a higher PLGA concentration. Three types of microspheres including porous

hollow core with thin porous shell (denoted by hollow in brief) and solid structures were finally selected for

in vitro

drug release tests. Bovine serum albumin (BSA) was chosen as model drug and encapsulated within the microspheres. The BSA encapsulation efficiency of porous

hollow and solid microspheres was respectively 90.4%

79.8% and 0. And the ultimate accumulative release was respectively 74.5%

58.9% and 0. The release rate of porous microspheres was much slower than that of hollow microspheres. The experiment results indicated that microspheres with different porous structures showed great potentials in controlling drug release behavior.