Antioxidant activity of crude（exopolysaccharides,EPS）and purified（EPS-1）extracellular polysaccharides from Cordyceps militaris BYB-08 were studied.The result showed that both crude and purified polysaccharides had scavenging activity against DPPH radical,·OH,O2-·,ferrous ion chelating ability and total reducing capacity (T-AOC).The scavenging rates of EPS and EPS-1 on DPPH radical at 10 mg/mL were 96.07% and 95.51%.The scavenging rates of EPS and EPS-1 on ·OH were 74.00% and 68.39%.The ferrous ion chelating capacity,scavenging rates of O2-·and the reducing power of EPS and EPS-1 were 54.12%,28.13%,75.10%,62.12%,62% and 54%,respectively.The crude polysaccharides EPS showed stronger antioxidant properties than purified polysaccharides EPS-1.