Cancer is the second leading cause of death in the United States and a leading cause of morbidity and mortality worldwide. A promising area of cancer research is focused on chemoprevention by nutritional compounds. Epidemiological studies have shown a strong negative correlation between fruit, vegetable and spice intake and rates of cancer. Although individual active compounds have demonstrated significant anti-cancer activity, an emerging area of research is focusing on the combination of multiple dietary compounds on cancer that act synergistically to exert greater effects. In the current study, we evaluated potential synergistic effects of capsaicin, an active compound from red chili peppers, in combination with 3,3'-Diindolylmethane (DIM), from cruciferous vegetables. A synergistic induction of apoptosis and inhibition of cell proliferation was observed in multiple cancer cell lines treated with combination of capsaicin and DIM. We also observed that these two compounds activated transcriptional activity of p53 and NF-kB synergistically. Combination treatment stabilized nuclear p53 and up- or down-regulated expression of several target genes that are downstream of NF-kB and p53. The present study suggests capsaicin and DIM work synergistically to inhibit cell proliferation and induce apoptosis in colorectal cancer through modulating transcriptional activity of NF-kB, p53 and expression of their target genes associated with apoptosis and cell cycle.