Bolbostemma paniculatum (Maxim.) Franquet (Cucurbitaceae) is a traditional Chinese medicinal plant (1), from which tubeimoside 1 was isolated. The antitumor activity and toxicity of tubeimoside 1 was investigated in vivo and in vitro. The results showed that tubeimoside 1 exerts potent anti-tumor activity with low toxicity. The compound inhibited DNA synthesis and induced phenotypic reverse transformation of tumor cells. Tubeimosides isolated from Bolbostemma paniculatum, C-16 hydroxyl group of tubeimoside II plays an important role in enhancing biological activity of tubeimoside II and in decreasing its toxicity. The difference of chemical structure in B and/or C position between tubeimosides III and II plays an important role in enhancing biological activity and toxicity of tubeimoside III. Therefore tubeimosidre II may be the most promising agent for cancer chemoprevention and chemotherapy among tubeimosides I, II, and III.