Five new prenylated flavonoids, maackiaflavanone A (1), maackiaflavanone B (2), maackiapentone (3), maackiapterocarpan A (4), maackiapterocarpan B (5) along with eleven known flavonoids were isolated from the stem bark of Maackia amurensis. The structures of the new compounds were elucidated by spectroscopic methods. The cytotoxicities of compounds 1-4, 6, 8-12 and 14-16 against four human cancer cell lines, A375S2, HeLa, MCF-7 and HepG2, were tested by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Among the compounds tested, compound 2 showed the strongest cytotoxic activity with IC(50) value of 7.8 microM against A375S2 and euchrenone b(1) showed the most potent cytotoxicity with IC(50) value of 4.5 microM against HeLa.