Objective:To study the effect of aqueous extract of several kinds of herbs on human platelet aggregation and expression of P-selectin in vitro.Methods:Blood was collected from volunteers.Effects of the prepared water extracts of herbs on platelet aggregation were monitored on a Packs-4 aggregometer.The fluorescence intensity of water extracts of Caulis Spatholobi,Flos Carthami and Rhizoma Curcumae on the expression of P-selectin in human platelets of healthy persons was measured with flow cytometry.Results:Out of several herbs investigated,Flos Carthami and Rhizoma Curcumae potently inhibited platelet aggregation after incubation with platelet-rich plasma(PRP) for 15 min.Caulis Spatholobi,Flos Carthami and Rhizoma Curcumae inhibited adenosine-5’-diphosphate(ADP) or platelet activating factor(PAF)-induced platelet aggregation in PRP in a dose-dependent manner.In contrast to Flos Carthami and Rhizoma Curcumae,Caulis Spatholobi could not inhibit thrombin-induced platelet aggregation.Despite its inability to inhibit thrombin-induced platelet aggregation in PRP,Caulis Spatholobi had a greater anti-aggregating activity in PRP induced by ADP or PAF.Caulis Spatholobi and Flos Carthami showed significant inhibitory effects on the expression of P-selectin.Conclusions:Caulis Spatholobi,Flos Carthami and Rhizoma Curcumae have potent anti-platelet properties,and their inhibitory actions are mediated via different mechanisms.Caulis Spatholobi inhibited ADP-induced platelet aggregation but not by thrombin,indicating that its mechanism of action might be independent of the thromboxane pathway.The effect of Caulis Spatholobi and Flos Carthami were associated with suppressing the expression of P-selectin. Objective: To study the effect of aqueous extract of several kinds of herbs on human platelet aggregation and expression of P-selectin in vitro. Methods: the blood was collected from volunteers. Effects of the prepared water extracts of herbs on platelet aggregation were monitored on a Packs-4 aggregometer. The fluorescence intensity of water extracts of Caulis Spatholobi, Flos Carthami and Rhizoma Curcumae on the expression of P-selectin in human platelets of healthy persons was measured with flow cytometry. Results: Out of several herbs investigated, Flos Carthami and Rhizoma Curcumae potently inhibited platelet aggregation after incubation with platelet-rich plasma (PRP) for 15 min. Caulis Spatholobi, Flos Carthami and Rhizoma Curcumae inhibited adenosine-5’-diphosphate (ADP) or platelet activating factor (PAF) -induced platelet aggregation in PRP in a dose-dependent manner. In contrast to Flos Carthami and Rhizoma Curcumae, Caulis Spatholobi could not inhibit thrombin-induced platelet aggregation. Despi te its inability to inhibit thrombin-induced platelet aggregation in PRP, Caulis Spatholobi had a greater anti-aggregating activity in PRP induced by ADP or PAF. Caulis Spatholobi and Flos Carthami showed significant inhibitory effects on the expression of P-selectin. Conclusions: Caulis Spatholobi, Flos Carthami and Rhizoma Curcumae have potent anti-platelet properties, and their inhibitory actions are mediated via different mechanisms. Caulis Spatholobi inhibited ADP-induced platelet aggregation but not by thrombin, indicating that its mechanism of action might be independent of the thromboxane pathway The effect of Caulis Spatholobi and Flos Carthami were associated with suppressing the expression of P-selectin.