Abstract: An acidic polysaccharide named EAP from Auricularia auricular-judae cultivated on Eleutherococcus senticosus was purified by iron chromatography and gel chromatography.The chemical composition and structure of EAP were analyzed by high performance liquid chromatography ( HPLC) and fourier transform infrared spectoscopy ( FT-IR) .The immunomodulatory effects of EAP on RAW264.7 macrophage were investigated by determining the production of NO and secretion of cytokines ( IL-6, IL-10, and TNF-α) . The result showed that EAP was an acidic polysaccharide with a molecular weight of 925.9 k Da and a βconfiguration.It was composed of mannose, glucose, glucuronic acid, xylose and galactose in the mole ratio of 64.8∶ 14.7∶ 14.2∶ 3.2∶ 2.0.At 50~250 μg/m L, EAP not only was cytotoxic to RAW264.7 cells, but also could significantly promoted the cell viability ( p <0.01) . The secretion of NO and IL-10 induced by EAP at 50 μg/m L was significantly improved ( p < 0.01) , reached17.2 μmol/L and 171.5 pg/m L, respectively.Moreover, EPA at 200 μg/m L significantly promoted the secretion of TNF-α and IL-6 ( p < 0.01) .It was concluded that the acidic polysaccharide from Auricularia auricular-judae cultivated on Eleutherococcus senticosus had good potential of immune enhancement.