The chromatographic separation of the MeOH extract from the twigs of Acer tegmentosum led to the isolation of ten phenolic compounds. The structures of these compounds were determined using spectroscopic methods as 3,7,3',4'-tetramethyl-quercetin (1), 5,3'-dihydroxy-3,7,4'-trimethoxy flavone (2), 2,6-dimethoxy-p-hydroquinone (3), (-)-catechin (4), morin-3-O-alpha-L-lyxoside (5), p-hydroxy phenylethyl-O-beta-D-glucopyranoside (6), 3,5-dimethoxy-4-hydroxy phenyl-1-O-beta-D-glucoside (7), fraxin (8), 3,5-dimethoxy-benzyl alcohol 4-O-beta-D-glucopyranoside (9) and 4-(2,3-dihydroxy propyl)-2,6-dimethoxy phenyl beta-D-glucopyranoside (10). The compounds were examined for their cytotoxic activity against five cancer cell lines. Compound 3 exhibited good cytotoxic activity against five human cancer cell lines with ED50 values ranging from 1.32 to 3.85 microM.