A new polyacetylene compound which has strong cytotoxic activity against L1210 cell, was isolated from Korean ginseng roots. The structure was determined to be heptadeca-1-ene-4,6-diyne-3,9-diol-10-acetate (10-acetyl panaxytriol, $ED_{50};=;1.2;{mu}g/ml$). The cytotoxicities of this compound and acetyl panaxydol lower than their starting substances, panaxytriol and panaxydol. The presence of one for the decreases in the cytotoxicities.