Anti-fatigue effect of polysaccharide from Radix astragali was investigated. 96 male mice were divided into the following 4 experimental groups: low-dose treated group 50 mg / kg polysaccharide(LPG), medium-dose treated group 100 mg / kg polysaccharide(MPG),high-dose treated group 200 mg / kg polysaccharide(HPG),and dH2 O control group(CG) for 28 consecutive days. The loading-weight exhausting swimming time, blood lactic acid, liver glycogen, SOD and GSH-Px concent in mice were determined. Results showed that polysaccharide from Radix astragali would significantly inhibit fatigue, which extended the loading-weight exhausting swimming time of mice, effectively delayed the increase of blood lactic acid, increased the storage of tissue glycogen, up-regulated SOD and GSH-Px activity during exercise and prevented oxidative stress.