Astragalus Polysaccharide (APS), an active component, was isolated from the radix of Astragalus membranaceus Bge var. mongholicus (Bge) Hsiao, and the effects of APS on E. coli endotoxin-induced liver damage were investigated in mice. The results showed that when mice were pretreated with APS (30, 60, 100 mg.kg-1.d-1 x 7d, ip), the survival rate of endotoxin intoxicated mice was increased the lowering of ATP levels and adenylate energy charge in mouse liver could be prevented. APS 100 mg.kg-1 could protect the mice from death on endotoxin (25 mg.kg-1) intoxication; and the level of ATP, the value of adenylate energy charge in the protected mouse liver were almost recovered to normal range. The effects of APS were shown to be dose-dependent. Concomitantly, the increase of MDA and decrease of GSH in mouse liver could be corrected by APS pretreatment. The results revealed that APS has an antioxidative action. An ultramicroscopic examination showed that the injury of the bio-membrane and the crest of mitochondria were ameliorated by APS pretreatment. These findings suggest that the protective effects of APS on E. coli endotoxin intoxicated mice may be due to its antioxidative action to protect the mitochondria bio-membrane, therefore, the adenylate metabolism is improved in mouse liver.