Abstract: In this study,the extraction temperature,extraction time,ratio of water to material and times on the extraction of polysaccharide from Lyophyllum decastes(Fr.)Singer were optimized by single factor and response surface method. The antioxidant activity of polysaccharide from Lyophyllum decastes(Fr.)Singer was further studied.The results showed that when the extraction temperature was 89 ℃,the extraction time was 3 h,the ratio of water to material was 30∶1 (mL/g)and the extraction times was 2,the yield of polysaccharide reached 5.38%±0.12%,which was close to the predicted value.The antioxidant activity of polysaccharide showed a dose-dependent manner within the range of 0~1.0 mg/mL,and the scavenging activities of DPPH and ABTS radical reach 45.87%±2.12% and 76.49%±1.56%,respectively,when at concentration of 1.0 mg/mL.The IC₅₀ values of DPPH and ABTS radical scavenging activities were 1.4 and 0.44 mg/mL,respectively,indicating polysaccharides from Lyophyllum decastes(Fr.)Singer exhibited positive antioxidant capacity.