Objective: The investigate effects of astragalus polysaccharide (APS) segments with different molecular weight (Mw) on immunoregulation. Method: The systematic immunodepressie mice were prepared through subcutaneous injection of cyclophosphamide (CY) at the dose of 25 mg ·kg-1

and APS segments with different Mw (157.7

69.9

22.4

13.2

1.4×103) were then ig administrated for 14 days by the dose of 139 mg ·kg-1. Serum hemolysin

DNFB induced mice ear edema and the phagocytosis of peritoneal macrophage were used to characterize the effects of samples on cellular immunity

humoral immunity and non-specific immunity respectively. Mucosal immunodepressive mice were prepared through subcutaneous injection of CY (50 mg ·kg-1)

and were administrated with the same samples as above. Secreted immunoglobulin A (sIgA) in lung and intestine irrigating solution

alteration of peyer’s patches in intestine were observed to study the effect of samples on mucosal immunity. Result: Phagocytosis index

phagocytosis rate

ear edema

serum hemolysin level and sIgA level in intestine and lung were increased by total APS and samples with larger Mw to different extent

and the 157.7×103 APS behaved the strongest effects for most indicators. Conclusion: APS with larger molecule weight could improve both systematic and mucosal immunity in immunodepressive mouse

and its effects were stronger than APS with lower melocule weight. This molecular segment of polysaccharide might be the main active substances of astragalus responsible for its immunomodulatory effect.