Abstract: Polydatin is 3,4′, 5-trihydroxystilbene-3-β-mono-D-glucoside isolated from Polygonum cuspidatum Sieb et Zucc. The actions of polydatin 0.6, 2.6 and 10.4 μg/ml in vitro and 5 mg/kg in vivo on platelet aggregation were studied in rabbits. Polydatin was shown to inhibit ADP, arachidonic acid, Ca²⁺ and clonidine-induced platelet aggregation significantly. In vitro, the rates of inhibition were 18～36% (ADP-induced), 26～58% (arachidonic acid-induced) and 42～64% (Ca²⁺-induced). However, the inhibition of thrombin-induced aggregation was not statistically significant. In in vivo experiments, 5, 30 and 60 min after iv polydatin, the rates of inhibition were 52～63% (ADP-induced), 59～76% (arachidonic acidinduced) and 10～16% (Ca²⁺-induced) respectively.