Abstract: Crude polysaccharides from synnemata of Cordyceps cicadae(BGS)were obtained by water extraction and alcohol precipitation method. The crude polysaccharides were purified by DE-52 cellulose chromatography and Sephadex G-100 chromatography.The antioxidant properties of BGS fractions were evaluated by four in vitro antioxidant assays,including 1,1-diphenyl-2-picrylhydrazyl(DPPH)free radical scavenging assay,reducing power,hydroxyl free radical scavenging assay,and chelating ability of ferrous ions.Hepatoprotective effect of fraction BGS-2 was evaluated by acyclophosphamide-induced liver injury model in mice.The results revealed that fraction of BGS-2 exhibited antioxidant capacity in a dose-dependent manner in all assays,and BSG-2 had the best antioxdant. The EC₅₀ values of DPPH every free radical scavenging activity,hydroxyl free radical scavenging activity and and chelating ability of ferrous ions for BGS-2 were 0.45,0.73 and 2.06 g/L,respectively. The increasing serum alanine aminotransferase and aspartate aminotransferase levels of mice after cyclophosphamide treatment were extremly inhibited by BGS-2(P<0.01). Furthermore,BGS-2 could effectively increase the superoxidase dismutase,catalase and glutathione peroxidase activities,and significantly inhibit the increasing in malondialdehyde level(P<0.01). These results indicated that BGS-2 might be useful for ameliorating the hepatotoxicity caused by cyclophosphamide partly due to boosting the activities of antioxidant enzymes,scavenging free radicals and chelating of ferrous ions.