Abstract: Objective: This study was designed to investigate the chemical characterization and antitumor effects of Pleurotus eryngii polysaccharides( PEP). Method: A novel water- soluble PEP was purified from P. eryngii by Cellulose DEAE- 52 and Sephadex G- 100 chromatography to get one fractions,namely PEP- 2. The monosaccharides composition and molecular weight of PEP-2 was analyzed by HPLC.Colorimetric MTT assay was performed to assess cell viability of Hep G- 2 cells treated with PEP- 2. The change in Hep G- 2 cell normal morphology was observed by DAPI staining.Result: HPLC analysis showed that PEP-2 was heteropolysaccharides mainly composed of glucose with the average molecular weights of 4.63 × 10~5 u. The antitumor activities of the polysaccharides against human hepatoblastoma Hep G- 2 cells were studied in vitro,and PEP- 2 showed strong growth inhibition against Hep G-2 cells.DAPI staining showed that the nucleus of untreated control cells was large and round without condensation or fragmentation,whereas the nucleus from the PEP- 2 treated cells was condensed and fragmented.Conclusion: It was a major breakthrough bringing new insight of the potential use of the P.eryngii polysaccharides as health- care food to provide significant natural defense against human cancer.