Korean ginseng, Panax ginseng Meyer (P. ginseng), has been used as a traditional oriental medicine to treat illness and promote health for several thousand years. Ginsenosides are the main constituents for the pharmacological effects of P. ginseng. Since several ginsenosides, including G-Rg3 and G-Rp1, was reported the anti-platelet activity, here we investigated the ability of G-Rp4 to modulate ADP-induced platelet aggregation. The ginsenoside Rp4 (G-Rp4), a similar chemical structure of ginseoside Rp1, was prepared from G-Rg1 by chemical modification.