Curcumin is a major active component of Curcuma aromatica salisb, which has been shown to inhibit proliferation of a wide variety of tumor cells. In this study, the molecular mechanisms of curcumin inducing apoptosis in human hepatoma SMMC-7721 cells were examined. We find that curcumin inhibits the growth of SMMC-7721 cells significantly in a concentration-depenent manner, with typical apoptotic morphological changes of cellular nuclei. Annexin-V/PI double staining detected by flow cytometry and expression of the relative apoptotic proteins (Bax, Bcl-2 and caspase-3) revealed a strong apoptosis-inducing competent of curcumin in SMMC-7721 cells. Curcumin increased the expression of bax protein while decreasing that of bc1-2 protein significantly. The results suggest that curcumin induction of apoptosis involves modulation of bax/bcl-2 in SMMC-7721 cells and provide a molecular basis for the development of naturally compounds as novel anticancer agents for human hepatomas.