Abstract: A novel intracellular polysaccharide,named HSIPS2,from Hirsutella sinensis was obtained by hot water extraction and alcohol precipitation,and then purified using DEAE-Sepharose Fast Flow chromatography and Sephacryl S-100 gel column chromatography. Its chain conformation and antioxidant activity were determined.The result showed that HSIPS2 was composed of glucose,galactose,mannose,and ribose with a molar ratio of48.52 ∶6.58 ∶5.17 ∶1.0. It was proved to be a novel lower dispersion polysaccharide with uniform molecular of1.463×10~4g/mol,and the purity was 99.82%. In 0.1 mol/L Na NO_3 aqueous solution,HSIPS2 existed as flexible chain conformation. The parameters of Rh,ML,q and d were 2.3 nm,334.05 nm~/(-1),0.70 nm,and 0.69 nm respectively.Moreover,the IC_(50) of its hydroxyl radical scavenging activity was identified to be 0.749 mg/m L and the value of ORAC was calculated to be 872.80 μmol TE/g. Hence,it was undoubtedly demonstrated that HSIPS2 exhibited potent antioxidant activity.