Twenty methanolic extracts from Thai spice powder (anise, cardamom, chilli, Chinese key, cinnamon, clove, coriander, cumin, deeplee, dill, fennel, galangal, kencur, lemongrass, ginger, nutmeg, oregano, pepper, safflower, and turmeric) were screened for pro-oxidative activity using a lecithin-liposome model system. The oxidative stress was induced by four systems: (I) non-metal induction; (II) FeCl3/H2O2/EDTA; (III) FeSO4/ascorbate; and (IV) CuSO4/H2O 2. Of these spices, safflower, lemongrass, and nutmeg extracts showed the pro-oxidative activity observed by thiobarbituric acid reactive substance elevation. Since pro-oxidation were metal dependent, hydroxyl radical formation was investigated by monitoring fluorescence products from benzoate hydroxylation. The formation of hydroxyl radical was confirmed with the fluorescence detected and the suppression due to addition of mannitol, a hydroxyl radical scavenger.