Panaxadiol (PD) from Korean red ginseng C.A. Meyer did not control the concentration of cytosolic free $Ca^{2+}$ influxes by thrombin (5 $mu$/ml). However, PD strongly inhibited the synthesis of thromboxane. $A_2$ (TX$A_2$) in the aggregation of human platelets induced by thrombin (5 $mu$/ml). These rexults suggest that PD blocks the any Pathway transforming to TX$A_2$ from arachidonic acid (AA) which release out of plasma membrane phospholipids by $Ca^{2+}$-dependent phospholipase C or phospholipase $A_2$. It may be also concluded that PD has the antiplatelet function by inhibiting the synthesis of TX$A_2$, which known to be the potent stimulator of the aggregation of human platelet.