The nightshade(Solanum nigrum Linn.) has been widely used in Chinese traditional medicine as a remedy for the treatment of digestive system cancer. The anti-tumor activity of solanine, a steroid alkaloid isolated from the nightshade has been demonstrated. To observe the effect of antitumor and mechanism of solanine. The MTT assay was used to evaluate the IC50 on the 3 digestive system tumor cell lines; The effect on the morphology was observed with a laser confocal microscopy; The rate of apoptosis and the cell cycle were measured using flow cytometry. The results show the IC50 for HepG2, SGC-7901, and LS-174 were 14.47, >50, and >50 mu g/ml, respectively; The morphology of cells in the negative control was normal; For the treated groups, typical signs for apoptosis were found. The rate of apoptosis in HepG2 cells induced by solanine was found to be 6.0%, 14.4%, 17.3%, 18.9%, and 32.2%, respectively. Observation of the cell cycle showed that cells in the G(2)/M phases disappeared while the number of cells in the S phase increased significantly for treated groups. Therefore, the solanine could induce apoptosis in HepG2 cells.