We investigated the effects of plant vinegar on platelets and blood coagulation system. Plant vinegar inhibited in vitro platelet aggregation in a concentration dependent manner, when platelets were activated by thrombin and collagen. In addition, plant vinegar showed inhibitory effects on the serotonin secretion induced by thrombin in a concentration dependent manner. However, treatment with plant vinegar to platelets did not induce any cytotoxicity, as determined by the release of lactate dehydrogenase. Plant vinegar did not change the coagulation parameters such as activated partial thromboplastin time (aPTT) and prothrombin time (PT) using rat citrated plasma. In vivo study revealed that, treatment with plant vinegar prolonged the bleeding time from mouse tail. All these results suggest that plant vinegar might improve blood hemostasis mediated via anti platelet activities.