Bioassay-guided fractionation of methanolic extracts of Mundulea chapelieri resulted in the isolation of two new flavonoids, isomundulinol (1) and 3-deoxy-MS-II (2), in addition to the eight known flavonoids 8-(3,3-dimethylallyl)-5,7-dimethoxyflavanone, MS-II, mundulinol, mundulone, munetone, rotenolone, rotenone, and tephrosin, and one known sesquiterpenoid, 8alpha-acetoxyelemol. The structures of the new flavonoids 1 and 2 were determined by 1D and 2D NMR experiments. All the isolated compounds were tested for cytotoxicity against the A2780 human ovarian cancer cell line; rotenolone and rotenone were the most potent compounds isolated, with IC(50) values of 0.5 and 0.7 microg/mL, respectively.