Vatdiospyroidol (1), a novel cytotoxic resveratrol tetramer, was isolated from the stems of Vatica diospyroides Sym. (Dipterocarpaceae) by bioassay-guided fractionation monitored with a human oral epidermoid carcinoma (KB) cell line. Another novel resveratrol tetramer, vaticaphenol A (2), was obtained as a noncytotoxic constituent, along with the known compounds, bergenin, betulin, betulinic acid, mangiferonic acid, and (E)-resveratrol 3-O-β-d-glucopyranoside. The structures of compounds 1 and 2 were elucidated by spectral analysis, including 1D and 2D NMR experiments, and by molecular modeling.