Objective To extract,isolate and identify the polysaccharide from ginseng,and to investigate its anti-tumor activity in vitro. Methods The ginseng polysaccharide was obtained through water extraction and ethyl alcohol deposition method. Use the Sevage method to remove the protein in the crude polysaccharide. The structural characteristics of the polysaccharide were determined by FT-IR spectra.The RM-1 and HeLa cells were divided into control group and different concentrations (0,50,100,200,300,400 and 500 mg·L-1 )of ginseng polysaccharide groups. The survival rates of the cells in various groups were detected by MTT method. The indirect killing effects of ginseng polysaccharide with different concentrations (0,50,100,200,300,400 and 500 mg·L-1 )on the cancer cells were determined by CTL test. Results The extraction rate of ginseng polysaccharide was 8.7 6% and the structural characteristics demonstrated that the main component of the extract was polysaccharide.The result of MTT showed that there were no significant differences of the survival rates of RM-1 and HeLa cells between different concentrations of ginseng polysaccharide groups after treated for 24 h compared with control group (P>0.05).The result of CTL test showed that the cytototic LHD release rates in different concentrations of ginseng polysaccharide groups were increased significantly (P<0.05)compared with control group;with the increase of ginseng polysaccharide concentration, the cytotoxic LDH release rates were increased firstly and then were decreased.When the concentration of ginseng polysaccharide was 100 mg·L-1 ,the cytotoxic LDH release rate was the biggest.Conclusion Ginseng polysaccharide can indirectly inhibit the growth of the tumor cells by activating T cells and play an anti-tumor effect.