Abstract: Optimization of fermentation medium for extracellular polysaccharides (EPS) and biomass by Lentinus edodes was studied by the method with Plackett-Burman design, the steepest ascent experiment and Box-Behnken design. The Letinous edodes 808 was used as the test material, for study the effect of liquid fermentation medium on the extracellular polysaccharide and mycelial biomass of Lentinula edodes. The results showed that the best medium combination for EPS were (g/500 m L) sucrose 7.18, corn meal 15.00, wheat bran 14.05, yeast extract 0.35, KH2PO40.50, Mg SO4·7H2O 0.50, natural p H. In this condition, EPS yield was 0.967 g/500 m L.The best medium combination for biomass yield were (g/500 m L) sucrose 7.18, corn meal 15.00, wheat bran 14.05, yeast extract 0.35, KH2PO40.75, Mg SO4·7H2O 0.50, natural p H.In this condition, biomass yield was 28.146 g/500 m L.All of the EPS yield and the biomass yield in the fermentation medium increased 12.44% and 11.00% as compared with that in the initial medium. This results could provide a theoretical basis for fermentation pilot production of Lentinus edodes.