Abstract: In this experiment, Lentinula edods (L. edodes) was used as carrier, with Na₂SeO₃ as the selenium source, to optimize the fermentation conditions of polysaccharide from Se-enriched L. edodes ant its antioxidant activity was studied. The effects of culture medium pH, sterling condition of selenium, selenium relenishing time, selenium concentration and incubation duration to polysaccharide form Se-enriched L. edodes were investigated by single factor experiment. The process parameters were optimized using a Box-Behnken experimental design coupled with response surface methodology. Polysaccharide from Se-enriched L. edodes was obtained under optimized conditions and its antioxidant activity was discussed by DPPH free radical scavening ability. The results showed that when the culture medium was pH4.16, 7.97 mg/L Na₂SeO₃ was added to the fermentation broth at 162 h, Na₂SeO₃ solution was sterilized by filtration, the incubation duration was 11 d, the yield of crude intracelluar polysaccharide in Se-enriched L. edodes reached 71.54 mg/100 mL;when the culture medium pH was 4.01, 6.68 mg/L Na₂SeO₃ was added to the fermentation broth at 191.5 h, Na₂SeO₃ solution was sterilized by filtration, the incubation duration was 11 d, the yield of crude extracellular polysaccharide in Se-enriched L. edodes reached 853.96 mg/100 mL. The results of DPPH free ladical scavening experiment showed that the antioxidative activities were as follows:intracellular polysaccharides in Se-enriched L. edodes > intracellular polysaccharides in L. edodes > extracellular polysaccharide in Se-enriched L. edodes > extracellular polysaccharide in L. edodes.Se-enriched not only increased the yield of polysaccharide form L. edodes, but also improved the antioxidant activity, better scavenging of the DPPH.