A total of 112 species of edible plants (122 samples) from Thailand were randomly collected, and their methanol extracts were screened for in vitro anti-tumor promoting activity using the inhibition test of Epstein-Barr virus (EBV) activation in Raji cells induced by 12-O-hexadecanoylphorbol-13-acetate (HPA, 40 ng/ml). It was found that 60% of these extracts inhibited EBV activation by 30% or more at a concentration of 200 mg/ml. Significantly, the ratio is markedly higher than that (26%) previously observed in common edible plants in Japan. Thus, physiological potentiality of edible Thai plants has been implied in terms of cancer chemoprevention.