The cytotoxic activity of 33,4,5-trihydroxybenzoic acid methylester and related compounds on the growth of normal cell lines, human skin melanoma cells and human oral epithelioid cell line were evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and 2,3-bis-[2-methoxy-4-nitro-5-sulfo-phenyl]-2-H-tetrazolium-5-caboxanilide (XTT) methods. 3,4,5-Trihydroxybenzoic acid methylester decreased the cell viability of human skin melanoma cells and human oral epithelioid cells shown by the MTT method and the cell adhesion activity of human skin melanoma cells and human oral epithelioid cells shown by the XTT method. In light microscopy, 100 ${mu}M$ 3,4,5-trihydroxybenzoic acid methylester showed the highest cytotoxic activity. These results suggest that 3,4,5-trihydroxybenzoic acid methylester has a potential anticancer activity.