Panax ginseng has been extensively used in the traditional oriental medicine as a restorative, tonic and Prophylactic agent. Recently, several reports regarding to anticancer effects of Panax ginseng has accumulated. These studies emphasized the fact that the anticancer activities might be due to a glycoside group called ginsenoside or pan.u saponin which has a water soluble characteristic. However, the authors and collaborates demonstrated that a highly lipid soluble component in extract of Panax ginseng roots contains a considerable cytotoxic activities against marine leukemic cells (L1210, P388) and human censer cells (HRT-18, HT-29, HCT48). This study was devised to observe the cytotoxic activities of Petroleum-ether extract of Panax giuseng roots (crude GBD and its Partially Purified fraction from silicic acid column chromatography (7 : 3 GX) against sarcoma-180 (5-180) and Walker carcinosar- coma 256 (Walker 256) in vivo, and murine leukemic Lymphocytes (L1210) and human rectal cancer cells (HRT-18) and human colon cancer cells (HT-29 and HCT48) in vitro. Each cell-line was cultured in medium containing serial concentration of the crude GX or 7 : 3 GX in vitro. A highly lipid soluble compound in the extract of Panax ginseng root was cytocidal to murine leukemic cells and human colon and rectal cancer cells in vitro. In the meantime, ginseng saponin derivatives did not have cytotoxic effects at its corresponding concentration. The growth rates of the cancer cells in medium containing ginseng extracts were inhibited gradually to a significant degree roughly in proportion to the increase of the extract concentration. The cytotoxic activity of 7 : 3 GX was about 3 times more potent than that of crude GX, one unit of cytotoxic activity against L1210 cells being equivalent to 2.54 Ug and 058 Ug for the crude GX and 7 : 3 GX, respectively. The Ri value of the active compound on silica- gel thin layer chromatography with petroleum-ether/ethyl ether/acetic acid mixture (90 : 10 : 1, v/v/v) as a developing so lvent was 053. While, the Panaxydol and Panaxynol as active compounds were purified from Petroleum-ether extract of Panax ginseng root by Drs. Ahn and Kim, and author found out that the one unit of cytotoxic activity of the Panaxydol and Panaxynol against L1210 cells being equivalent to 056 Ug and 0.3918 respectively. The survival times of mice inoculated with S-180 cells were extended about 1.5 to 2 times by the 7 : 3 GX treatment compared with their control group. The significantly decreased hemoglobin values of rats after inoculation with Walker 256 were recovered to normal range by oral administration of the crude Gt The synthetic levels of protein, DNA and RNA in human colon and rectal cancer cells were significantly diminished by treatment with the crude GX, which can explain a part of the origin of its anticancer activity.