Abstract: In order to study the effects of Isatis radix polysaccharide MPEG-PLA Block Copolymers Microspheres on immunity of mice. Mice were injected with the Isatis radix polysaccharide MPEG-PLA Block Copolymers Microspheres prepared in Lab and measured the blood routine indicatrix such as WBC and TLC, total IgG levels and phagocytic activity of peritoneal macrophages. The results indicated that the immune indices of experimental groups with the three dose were enhanced compared with the control group after injection 7days and 14 days, in the microsphere group, the effect of the EG of 20mg Isatis radix polysaccharide MPEG-PLA Block Copolymers Microspheres on immunity was the best, in the seventh day and fourteenth day , the WBC and TLC of the mice was (10.96±0.46), (11.03 ±0.35) and (8.73±0.51) , (9.44 ±0.42), the IgG level of the mice was (33.541±0.458) and (32.713±0.481), the phagocytic index and phagocytic percentage of the mice respectively achieved to (56±2.16) and (1.61±0.04). The Isatis radix polysaccharide MPEG-PLA Block Copolymers Microspheres could enhance the immune function, although the short-term immune function of the microspheres was lower than Isatis radix polysaccharide, but could achieve to long-term immune function.