Phytophthora cactorum and P. parasitica formed oospores on basal medium supplemented with corn oil or crude soybean lecithin. The non-saponifiable fraction from these two supplements were stimulatory to oospore formation of both fungi, but the saponifiables were stimulatory to only P. cactorum. When the non-saponifiables were subjected to Florisil column chromatography, the fraction eluted with 25% diethyl ether in hexane was the most stimulatory. Thin layer chromatography (TLC) separated this fraction into three active bands. Among them, the two non-digitonide TLC bands were further separated by high performance liquid chromatography (HPLC), and the active fractions were isolated for gas chromatography-mass spectrometry (GC-MS) analysis. Compounds identified were 3-eicosyne, β-farnesene, tetradecane (2, 6, 10-trimethyl), docosane, hexadecanol (2-methyl), phytol, and pentatriacontane. Commercially available phytol tested was found to be highly stimulatory to oospore formation of both fungi. It was active even at the concentration of 1 ng/basal medium disc.