In order to further understand the mechanism of hemostatic action, a study of the effects of Ju San Qi (Gynura segetum) and Shen San Qi (Panax notoginseng) on the ultrastructure of the guinea-pig platelets with elctron microscope was carried out. The result shows that the 10% extract of Ju San Qi and Shen San Qi added to the blood caused in vitro stretching and pseudopodia of the platelets such as stickydeformative motion (Fig 2～6), bread Kage or partial dissolution of the platelet cellmembrane (Fig 2,7,8), and induced degranulation (α-granules etc.) (Fig 2～9).It is likely that these actions caused the platelets to release ADP and other hemostaticly active substance so as to achieve hemostatic effects. The effects of these two drugs on platelets were shown to be directly propotional to the amount of the drug added to the blood, The effects of both drugs are basically the same. The effects of these drugs on the ultrastructure of platelets are similar to those of thrombin.