Abstract: Dang-Gui (Angelica sinensis) has been used for the treatment of thromboangiitis obliterans and acute cerebral thrombolic diseases with favorable results. In this paper the effect of Dang-Gui and its ingredient ferulic acid on platelet aggregation and 5-HT release reaction in rats is reported.In vitro studies, rat platelet aggregation induced with adenosine diphosphate or collagen was inhibited by the aqueous extract of Dang-Gui (200～500mg/ml) and by synthetic ferulic acid (0.4～0.6mg/ml).Intravenous injection of Dang-Gui at a dose of 20 g/kg inhibited rat platelet aggregation. An inhibitory effect on platelet aggregation was also observed when sodium ferulate was administered intravenously at doses of 0.1～0.2g/kg.The aqueous extract of Dang-Gui (500mg/ml) and sodium ferulate (1～2mg/ml) were shown to inhibit aggregation and release of ³H-5-HT labelled rat platelets induced by thrombin.The therapeutic effect of Dang-Gui in the treatment of cerebral thrombosis and thromboangiitis obliterans seems to be related to the inhibition of platelet aggregation and release of 5-HT from platelets.