Platelets are necessary for hemostasis as well as, involve in atherothrombosis, which is the major cause of cardiovascular diseases (CVD). Components in food which exhibit antiplatelet activity may promote health beneficial in people who have high risk of CVD. The major objective of this study is to evaluate antiplatelet activity of pomelo following two experiments. The first experiment, antiplatelet activity of juice and methanolic extract of pomelo from three cultivars; Thong Dee, Khao Yai and Khao Thang Kwa, were evaluated using models of ADP- and thrombin- induced platelet aggregation. The second experiment, platelet activity was studied in healthy volunteers before and 4 hours after consumption of pomelo (Thong Dee). Platelet aggregation study was performed with platelet-rich plasma and using turbidimetric method. The results demonstrated that juice and methanolic extract inhibited platelet aggregation by reducing both rate and maximum aggregation when ADP was used as agonist but not with thrombin. Flavonoids including quercetin, keampferol luteolin and their glucosidic derivatives did not showed inhibitory effect on plate aggregation although the high concentration up to 200 mM was used. Furthermore, consumption of pomelo did not affect platelet activity in healthy volunteers. In addition to antiplatelet activity, antioxidant activity of pomelo was evaluated. All of three cultivars exhibited potent antioxidant activity. Pomelo also inhibited formation of lipid radical formation in liposome and platelet, suggesting that antioxidant may partly contribute to antiplatelet activity. In conclusion, juice and methanolic extract of pomelo exhibited antiplatelet activity in ADPinduced platelet aggregation. Flavonoids were not active components for antiplatelet activity. Hence, others compounds should be considered. Consumption of 1 serving size of pomelo (200g) showed no effect on platelet function, suggesting that consumption of pomelo may not produce food and drug interaction in the patients under treatment of antiplatelet drugs. However, it is interested to evaluate the effect of long term consumption of pomelo in the people who have high risk of CVD.