Xanthorrhizol, a natural sesquiterpenoid compound isolated from Curcuma xanthorrhiza Roxb, has been known to inhibit the growth of human colon, breast, liver and cervical cancer cells. In this study, xanthorrhizol decreased cell viability, induced apoptosis and decreased the level of full-length PARP in SCC-15 oral squamous cell carcinoma (OSCC) cells. A decrease in cell viability and PARP degradation was not prevented by treatment with the caspase inhibitor Z-VAD-fmk in xanthorrhizol-treated cells. Xanthorrhizol treatment elevated intracellular Ca2+ and ROS levels in SCC-15 cells. Treatment with a Ca2+ chelator, EGTA/AM, did not affect xanthorrhizol- induced cytotoxicity, but cell viability was partly recovered by treatment with endogenous antioxidant, GSH, or hydroxy radical trapper, MCI-186. Furthermore, the viability of xanthorrhizol-treated SCC-15 cells was significantly restored by treatment with SB203580 and/or SP600125 but not significantly by PD98059 treatment. Xanthorrhizol-induced activation of p38 MAPK and JNK was blocked by MCI-186. Finally, xanthorrhizol suppressed the number of tumors in buccal pouches and increased the survival rate in hamsters treated with 7,12-dimethylbenz[a]anthracene. In conclusion, xanthorrhizol may induce caspase-independent apoptosis through ROS-mediated p38 MAPK and JNK activation in SCC-15 OSCC cells and prevent chemical-induced oral carcinogenesis. Therefore, xanthorrhizol seems to be a promising chemopreventive agent. Copyright © 2012 John Wiley & Sons, Ltd.