Cancer rates are increasing dramatically, and there is currently a strong emphasis on identifying biologically active substances with anti-cancer activity from traditional herbs, as these are thought to have less adverse side-effects than conventional chemotherapy. Here, we examined the effects of extracts of Orostachys japonicus A. BERGER (O. japonicus) on cancer cell proliferation and apoptosis, and investigated the underlying signaling pathways. Dried powdered O. japonicus was extracted with 95% ethyl alcohol and fractionated with a series of organic solvents, including n-hexane (hexane), dichloromethane (DCM), ethylacetate (EtOAc), n-butanol (BuOH), and water (H(2)O). These extracts were tested for anti-cancer activity on a range of cancer cells; of all these, the EtOAc soluble fraction showed the highest anti-cancer activity, which was most marked in AGS human gastric cancer cells. The EtOAc fraction inhibited the proliferation of AGS cells in a dose-dependent and time-dependent manner, by inducing apoptosis and cell cycle arrest, as evidenced by 4,6-diamidino-2-phenylindole (DAPI) staining, annexin V-fluorescein isothiocyanate staining, propidium iodide-labeling, and DNA fragmentation assays. Western blot analysis revealed that p53 and cleaved caspase-3 proteins were up-regulated, and B cell lymphoma-2 (bcl-2) protein and pro-caspase-3 were down-regulated, but bcl-2 associated x protein (bax) protein was not regulated, in response to treatment of AGS cells with the EtOAc fraction. However, the changes of pro-caspase-3 and cleaved caspase-3 could be abolished by the pan-caspase inhibitor Z-VAD-FMK. These results suggest the EtOAc fraction from O. japonicus has substantial anti-cancer activity in human gastric cancer cells.