This study was carried out for the identification and bioassay of bioactive compounds which isolated from Phyutolacca americana L. obtained results are summarized as follows: 1. Two biological active compounds were found from crude extracts of P. americana roots, using the systematic solvent fractionations, such as ethyl acetate fraction and butanol fraction. One biological compound was isolated from the ethyl acetate fraction with silicagel column chromatography, which was identified as a ${alpha}-spinasterol$ by spectral analysis of IR, H-NMR, C-NMR and MS. The other one is isolated from butanol fraction which was identified as phytolaccoside E by spectral analysis of IR, H-NMR, C-NMR and MS. 2. The ${alpha}-spinasterol$ and phytolaccoside E induced necrosis of primary root and resulted in death of the tested plant. These two compounds strongly inhibited to the growth of Mucor racemous and Phytophthora infestants but did not inhibited the growth of Colletotricum lagenarium and Fusarium oxisporum. 3. Cytotoxicity of the two biological active compound was exammined to the two different animal cancer cell lines (L1210, K562). The phytolaccoside E has some cytotoxical activity to the growth of cancer cell lines (L1210, K562) but $alpha$-spinasterol has not cytotoxical effect.