It has been reported that curcumin (diferuloylmethane) could inhibit growth of several types of malignant cells both in vitro and in vivo. However, the mechanism of its action is unknown. In this study, we investigated the inhibitory effects of curcumin on human colon carcinoma cell (Lovo) growth and its mechanism of action in vitro by means of growth assay, colony formation assay, MTT assay, cell cycle and apoptosis analysis. Curcumin inhibited cell growth in a dose-dependent manner. The ability of Lovo cells treated with curcumin to form colonies was depressed. MTT test showed that curcumin was cytotoxic to cells. Lovo cells treated with curcumin were largely accumulated in S, G2/M phase which prevented cells from entering the next cell cycle. Apoptosis induced by curcumin was confirmed by characteristic ladders and cellular morphological changes. Curcumin can inhibit Lovo cells growth and the cellular mechanism responsible for the action is to arrest the cell cycle in S, G2/M phase and to induce apoptotic cell death.