Abstract: The polysaccharide was extracted from Radix Paeoniae Alba by the method of water extraction and ethanol precipitation. The optimum extraction parameters of the polysaccharide were determined by orthogonal test and its chemical compositions was investigated. The molecular weight of the polysaccharide was analyzed by HPSEC-UV-MALLS-RI system, which monosaccharide composition and glycosidic linkage was investigated by GC-MS. The effect of the polysaccharides on RAW264.7 cells proliferation was determined by WST assay. The results showed that the optimum extraction parameters were as follows: the ratio of liquid to material was 25:1 mL/g, extraction temperature 85 ℃, extraction time 3.0 h, with the yield of 12.40%. The polysaccharide was composed of 96.2%±1.2% total sugar and 5.5%±0.6% protein, no sulfate and uronic acid, with the molecular weight and radius of gyration 2.3×10⁶ u and 234.9 nm, respectively. The polysaccharide mainly contained glucose with the linkage of →4)-Glu-(1→, which also could promote the proliferation of RAW264.7 cells at the concentrations of 2, 5, 10 μg/mL.It was nothing that the cell proliferation rate of the 10 μg/mL treatment group was significantly increased, which exhibitedsignificant difference with other groups (P< 0.05).