The seeds of Zizyphus jujuba (SZJ), a famous oriental traditional medicine, have been reported to exhibit diverse activities in biological systems including the cardiovascular system. However, little information is available on its antiplatelet activity. This study was undertaken to investigate the antiplatelet effects of the ethanolic extract of SZJ (ESZJ) and of its principal components jujuboside A and B. In the in vitro platelet aggregation study, ESZJ exhibited significant and concentration-dependent inhibitory effects on collagen-, thrombin-, and AA-induced platelet aggregation. In addition, ESZJ-treated mice showed significantly the prolongation of bleeding times and the protection against thromboembolic attack. A comparison of the effects of jujuboside A and B on platelet aggregation revealed that only jujuboside B had potent inhibitory effects on collagen-, thrombin-, AA-, and ADP-induced aggregation. Jujuboside B also exhibited superior protection on thromboembolic model. Furthermore, jujuboside B had a significant inhibitory effect on collagen-induced thromboxane A2 production in rat platelets. This study describes the antiplatelet effects of ESZJ and of its active component jujuboside B, and its findings suggest that these agents be considered as components of preventive and therapeutic herbal drugs targeting cardiovascular diseases associated with platelet hyperaggregation. Copyright © 2012 John Wiley & Sons, Ltd.