We examined the anticancer effects of limonin and imperatorin on various human cancer cells by MTT assay, and the results showed that imperatorin inhibited the cell growth of SNU 449 (liver cancer) and HCT-15 (colon cancer) cells in a dose-dependent manner, while limonin had less effect. Exposure of different concentrations of limonin and imperatorin caused morphological changes in cancer cells, but not in normal dermal fibroblast cells. Limonin and imperatorin induced apoptotic cell death concurrent to cell cycle arrest in SNU 449 and HCT-15 cells. Limonin and imperatorin up regulated proapoptotic protein Bax expression and down regulated anti-apoptotic protein Bcl-2 expression in a dose-dependent manner in HCT-15 and SNU 449 cells. In conclusion, our data demonstrate that limonin and imperatorin have anticancer potential which is associated with promoting cell apoptosis through expression of apoptosis-related proteins.