Vietnamese ginseng, Panax vietnamensis was recently found in central Vietnam, and regarded as a new botanical species. It was used in traditional folk medicine in hill tribes for the purpose of anti-fatigue and life saving. From the rhizome and root of this plant, 37 saponins including 14 new compounds were isolated. Some of them were common to other Panax spp., but the general yields in this species were very high. Among them, an ocotillol-type saponin majonoside-R2 (MR2) was remarkable in its yield (5.3%). Structural features of new saponins were briefly introduced. The biological effects of these saponins were studied in two ways, anti-stress effect and anti-tumor promoting effect; both activities were based upon the traditional usage of this crude drug. In psychologically stressed mice, the saponin fraction of Vietnamese ginseng significantly reduced stress-related disorders (reducing sleeping time, formation of gastric lesions) and MR2 was responsible for this effect. A possible mechanism for this effect was proposed. MR2 exhibited a significant inhibitory effect on Epstein-Barr virus early antigen (EBV-EA) induced by the tumor promoter phorbol acetate. MR2 also showed potent anti-tumor-promoting activity on mouse skin and hepatic tumors.