Garcinol, obtained from Garcinia indica, is a potent antioxidant. Its anticancer activity has been investigated; however, there is no published report on its action against prostate and pancreatic cancer cells. We have earlier reported its activity against breast cancer cells, and here we tested our hypothesis that garcinol could inhibit cell proliferation and induce apoptosis in prostate as well as pancreatic cancer cells. Using multiple techniques such as MTT, Histone-DNA ELISA, activated caspase assays, clonogenic assays and EMSA, we investigated the mechanism of apoptosis-inducing effect of garcinol in prostate (LNCaP, C4-2B and PC3) and pancreatic (BxPC-3) cancer cells. We found that garcinol inhibited cell growth of all the cell lines tested with a concomitant induction of apoptosis in a dose-dependent manner. Down-regulation of NF-κB signaling pathway appears to be the mechanism of apoptosis-induction because garcinol inhibited constitutive levels of NF-κB activity, which was consistent with down-regulation of NF-κB-regulated genes. A significant decrease in the colony forming ability of all the cell lines was also observed, suggesting the possible application of this compound against metastatic disease. In summary, our results provide pre-clinical evidence to support the use of garcinol against human prostate and pancreatic cancer, thus meriting its further investigation as a potential chemo-preventive and/or therapeutic agent.