The methanol extract of the twigs of Garcinia hombroniana, which showed strong LDL antioxidation and antiplatelet aggregation activities, was subjected to column chromatography to obtain 3,5,3′,5′-tetrahydroxy-4-methoxybenzophenone, 1,7-dihydroxyxanthone and eight triterpenoids, garcihombronane B, D, E and F, friedelin, glutin-5-en-3β-ol, stigmasterol and lupeol. The structures of the compounds were elucidated by spectroscopic methods. The compounds were evaluated for their ability to inhibit copper-mediated LDL oxidation and arachidonic acid (AA)-, adenosine diphosphate (ADP)-, collagen-induced platelet aggregation in vitro. Among the compounds tested, 3,5,3′,5′-tetrahydroxy-4-methoxybenzophenone and 1,7-dihydroxyxanthone showed strong inhibitory activity on LDL oxidation with half-maximal inhibitory concentration (IC50) values of 6.6 and 1.7 µm, respectively. 3,5,3′,5′-Tetrahydroxy-4-methoxybenzophenone exhibited strong activity on AA-, ADP- and collagen-induced platelet aggregation with IC50 values of 53.6, 125.7 and 178.6 µm, respectively, while 1,7 dihydroxyxanthone showed significant and selective inhibitory activity against ADP-induced aggregation with IC50 value of 5.7 µm. Of the triterpenoids tested, garcihombronane B showed moderate activity against LDL oxidation and garcihombronane D and F showed selective inhibition on ADP-induced platelet aggregation. Copyright © 2012 John Wiley & Sons, Ltd.