Abstract: A three - factor, three - level orthogonal array design was used to study the effects of three extraction conditions including temperature, time and solvent - to - solid ratio on polysaccharide yield. Intercellular polysaccharide was extracted from fermentation mycelium of Pholiota dinghuensis Bi. The activity of lysozyme in serum and spleen, immune organs index, swelling rate of ear and hemolysin in serum of mice were measured in vivo according to the animal models experiment.The results showed that the optimal conditions for the extraction of polysaccharide from Pholiota dinghuensis Bi ( PFPD) were 6h extractionat 90℃ and a solvent-to-solid radio 20mL /g, resulting in a polysaccharide yield of 8.95% . The PFPD intraperitoneal injected was able to overcome cyclophosphamide-induced immunosuppression.In addition, the spleen index, late onset allergic reaction of right ear degree, level of serum hemolysin and spleen, and serum lysozyme activity of the animals treated with different doses PFPD increased in a dose - dependent manner. The results suggested that the Pholiota dinghuensis Bi polysaccharide had some of immunomodulatory activity in vivo.