To develop a new protein delivery system for superoxide dismutase (SOD), biodegradable materials like poly(DL-lactide-co-glycolide) (PLGA), alginate, and chitosan were used for preparing PLGA microspheres and alginate-chitosan microspheres, which were used for encapsulating protein. Alginate-chitosan microspheres showed much higher entrapment efficiency (91.08% +/- 1.28%) than that of PLGA microspheres (36.42% +/- 1.81%). In vitro release study showed that SOD presented a sustained release character in the preparation of these biodegradable materials. After 15 days, 43.72% +/- 0.43% of protein was released from alginate-chitosan microspheres, while there was 62.96% +/- 3.95% of protein release from PLGA microspheres. However, alginate-chitosan demonstrated that it was a better material to control the burst release of protein from microspheres. Furthermore, SOD activity in microspheres was evaluated, and the results showed that microspheres protected the activity of protein to some extent. Finally, PLGA-alginate-chitosan complex microspheres were constructed and the release character in vitro demonstrated that this preparation could not only prolong the release of drug but also decrease the burst release.