The methanol extract of Euphorbia milii exhibited strong inhibitory effect on platelet aggregation in the cource of our search for anti-platelet component from succulent plants. Two components, components 1 and 2 were isolated from this plant. 1 was the mixture of 72% of 1-octacosanol (1a) and 28% of 1-triacontanol (1b), and 2 was identified as ${eta}-sitosterol$. 2 ($IC_{50}$: $195;{mu}M$, and $170;{mu}M$ respectively) was about two fold stronger than ASA ($IC_{50}$: $420;{mu}M$ and $340;{mu}M$ respectively) on both collagen and U46619 induced aggregation, while the effect of 1 to platelets was negligible.