Abstract: A water-soluble polysaccharide from root of Podophyllum Emodi was obtained through boiling water. The physical and chemical characteristics of the Podophyllum Emodi polysaccharides(PEP) was analyzed by filter paper chromatography and FT-IR. Stimulation test of PEP on splenic lymphocyte proliferation was performed in vitro. In vivo,on day 1,3,5 and 7, ten mice were given PEP at dose of 200 mg/kg BW by abdominal injection.The model of immune hypofunction was established by using dexamethasone, PEP(200 mg/kg BW) was given to investigate the effects of the polysaccharide on immune function and oxidative stress. The results showed that PEP is composed of glucose, fructose, mannose and arabinose. PEP stimulated the lymphocytes proliferation and induced the lymphocyte proliferation in cooperation with ConA in vitro. PEP improved the spleen index(P<0.05). PEP can significantly increase the descent activity of T-SOD and activity of antisuperoxide anion induced by dexamethasone（P<0.01）, and decreased the content of hydrogen dioxide and content of malondialdehyde(P<0.01), it can also significantly increase the activity of T-AOC（P<0.01）in vivo. It is concluded that the PEP may play an important role in modulating immune function and prevention of oxidative damage in immunological system.