Methanol extracts of Myrobalan (1), knots of Wisteria brachybotrys (2), fruits of Trapa japonica (3) and Coix seed (4) were assayed for their inhibitory effects on Epstein-Barr virus (EBV) activations by a short term in vitro assay in which lymphoblastoid cells (Raji) latently infected with EBV were used. The EBV activation by 12-0-tetradecanoylphorbol-13-acetate (TPA) and teleocidin B was inhibited markedly by 1 and 2 but only weakly by 3. Coix seed (4) was found to show a significant in vitro cytotoxic effect on the Raji cells. The methanolic extracts from four mixtures of the crude drugs i.e., 1 and 4, 2 and 3, 2 and 4, and 2, 3 and 4, gave more enhanced inhibitory effects on EBV activation, with less cytotoxicity. These inhibitory effects on EBV activation suggested that these crude drugs possess antitumor promoting activities.