Numerous human chemoprevention studies have demonstrated that non-steroidal anti-inflammatory drugs (NSAIDs) possess chemopreventive effects against a variety of malignant tumors. However, there have been many clinical studies on aspirin, but not ibuprofen, even though ibuprofen is one of the most clinically and safely used NSAIDs showing potent anti-inflammatory effects. Moreover, we reported that many chemopreventive agents enhance the apoptosis-inducing effects of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which is known to be crucial for cancer prevention. We, therefore, investigated whether ibuprofen enhances the cytocidal effect of TRAIL and found that ibuprofen markedly stimulated the apoptosis-inducing efficacy of TRAIL against human colon cancer HCT116 cells. As detected by western blot analysis and real-time RT-PCR, ibuprofen upregulated the expression of death receptor 5 (DR5), a TRAIL receptor. TRAIL-induced apoptosis enhanced by ibuprofen was effectively decreased by a caspase inhibitor and dominant-negative DR5. Noteworthy, co-treatment of ibuprofen with TRAIL did not enhance apoptosis in normal peripheral blood mononuclear cells (PBMCs). These results demonstrated that ibuprofen and TRAIL synergistically induced apoptosis in human colon cancer HCT116 cells but not in normal PBMCs, raising the possibility that ibuprofen may be promising as a safe chemopreventive agent against colon cancer.