Abstract: OBJECTIVE To isolate and purify an active polysaccharide of Momordica charantia L. and investigate its structural characterization and immunomodulatory and antitumor activities. METHODS A polysaccharides was isolated from Momordica charantia L. in hot water extraction followed by dialysis and purification through anion exchange cellulose chromatography and gel filtration chromatography， and its molecular weight was measured by high performance gel permeation chromatography. Additionally， Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) were used to determine its partial structural characterization， and its immunomodulatory and antitumor activities were measured by cell and molecular biological techniques and pharmacological methods. RESULTS A heteropolysaccharide named MCP-2 with molecular weight of 745 kDa was isolated and purified， which was shown to be consisted of rhamnose， galacturonic acid， galactose， xylose， and arabinose with corresponding molar ratio being 1.19∶15.97∶3.40∶0.73∶0.94. Furthermore， MCP-2 was found to promote the lymphocyte proliferation of normal mice and to raise the levels of NO， IL-1β and TNF-α produced by macrophage RAW264.7. Intriguingly， MCP-2 presented the antitumor activity against S180 cells in vivo as well. CONCLUSION All experimental data showed that MCP-2 had apparent immunologic enhancement and antitumor activities.