Objective To study the mechanism of killing and apoptosis-inducing effects of Capparis spinosa alkaloid (CSA) on human hepatocarcinoma cell line HepG2. Methods The killing effect of CSA on human hepatocarcinoma cell line HepG2 was studied by MTT method. Morphological observation of HepG2 cells was carried out by fluorescence microscope. Results The CSA had obvious cytotoxicity on the HepG2 in a dose-dependent manner and its IC50 value was 142.82 ?g/mL. The HepG2 cells showed the characteristic morphologic changes of apoptosis by the function of CSA and the apoptosis percentage is higher than that of the natural one. The progress of cells cycle from S phase to G2 phase had been blocked by CSA. The intracellular Ca2+ level had been increased by the function of CSA, which was positively related with drug concentration. Conclusion CSA has obviously killing and apoptosis-inducing effects on human hepatocarcinoma cell line HepG2 and calcium overload might also be invovled in these events.