Abstract: The effect of indole acetic acids (IAA) on biomass, extracellular polysaccharide (EPS) production and antioxidant activity of Cordyceps sinensis were studied in the present work. The results showed that the reasonable concentration of IAA could increase biomass and EPS production of Cordyceps sinensis. Biomass and EPS production were increased first and then decreased with the increase of IAA. Both of biomass and EPS production reached the highest content at 2.5μg/m L IAA, namely 18.3g/L and 2.9g/L, increased 6.3% and15.4% comparing no IAA, respectively. The appropriate concentration of IAA could also improve the antioxidant activity of EPS. The strongest scavenging effect on hydroxyl radical and DPPH of EPS were 58.9% and 56.6%at the concentrations of 1.0μg/m L and 2.5μg/m L, respectively.