Abstract: To research the extraction process of polysaccharides from fermented wheat bran,determine its monosaccharide components,and investigate its antioxidative activity in vivo,using water extraction and alcohol precipitation method to extract fermented wheat bran polysaccharides(FWBP),and the extraction conditions were optimized. The monosaccharide composition of FWBP was determined by precolumnderivatization HPLC. The rats were established as oxidative stress model by peritoneal injecting diquat. The rats were orally treated with FWBP at 100,200 and 400 mg/kg for 2 weaks,respectively. Effects of FWBP on the activities of total antioxidative capacity,catalase,glutathione peroxidase and superoxide dismutase,and the glutathione and malondialdehyde levels in the plasma and liver of rats were investigated. The results demonstrated that the optimum extraction conditions for FWBP were material/water ratio 1:20 (w/v,g/mL),extraction temperature 80 ℃ and extraction duration 30 min. The FWBP contained mainly mannose,rhamnose,glucose,galactose,xylose,arabinose and mycose with the molar ratio at 2.70:0.62:100.20:4.34:7.80:12.23:35.17. Compared with diquat induced oxidative-stress rats,pretreatment of rats with FWBP significantly increased the activities of CAT,SOD,GSH-Px and the levels of GSH whereas(p<0.05)decreased the levels of MDA in plasma and liver(p<0.05). In summary,FWBP exerted a protective effect against diquat-induced oxidative stress and would be worthy of becoming a potential dietary antioxidant.