OBJECTIVE： To study the anti-tumor effect of ethanol extract of Smilax trinervula and its different polar extract parts， and to provide reference for the screening of anti-tumor active parts. METHODS： MTT method was used to detect the inhibitory rates of different concentrations of ethanol extract of S. trinervula， its petroleum ether， ethyl acetate， n-butanol and water layer extract parts to the proliferation of human hepatocellular carcinoma cell line HepG2， human lung cancer cell line A549， human breast cancer cell line MCF-7 and MDA-MB-231， human cervical cancer cell line HeLa and human ovarian cancer cell line HO-8910. Semi-inhibitory concentration （IC50） was calculated. A total of 80 KM mice were subcutaneously inoculated with S180 cell suspension in right forelimb axilla to induce tumor-bearing mice model. The mice were randomly divided into 8 groups： e.g. model group （normal saline， twice a day， i.g.）， cyclophosphamide （positive drug） group （0.025 g/kg， once a day， i.p.）， S. trinervula ethanol extract high-dose， medium-dose and low-dose groups， ethyl acetate part of ethanol extract high-dose， medium-dose and low-dose groups （0.1， 0.05， 0.025 g/kg by extract， twice a day， i.g.）， with 10 rats in each group. The mice in each group were given medicine for consecutive 14 days. The inhibition rate， spleen index and thymus index of mice in each group were measured after fasting for 12 hours after the last administration. RESULTS： In vitro experiments showed that S. trinervula and different polar extracts inhibited the proliferation of 6 kinds of tumor cells in significant dose-effect manner， especially ethyl acetate part of ethanol extract. IC50 of it to tumor cells was 40-210 μg/mL， that of it to MCF-7， MDA-MB-231 and HeLa cells were 70.56， 83.58， 44.67 μg/mL， respectively. In vivo experiments showed that the tumor mass of mice were decreased significantly in each administrations （P＜0.05 or P＜0.01）， the tumor mass of mice in S. trinervula ethanol extract high-dose group， ethyl acetate part of ethanol extract high-dose and medium dose groups were significantly lower than cyclophosphamide group （P＜0.01）. The spleen index of mice was decreased significantly in cyclophosphamide group， S. trinervula ethanol extract high-dose group， ethyl acetate part of ethanol extract high-dose and medium dose groups， compared with model group （P＜0.01）； thymus index of mice in cyclophosphamide group was increased significantly， compared with model group and other administration groups （P＜0.01）. CONCLUSIONS： The ethyl acetate part of ethanol extract of S. trinervula has the best anti-tumor effect and less immunosuppressive effect.