The aim of this study was to investigate the effect of Paris saponin Ⅰ (PS Ⅰ ) on human gastric carcinoma cell growth and apoptosis and to explore the potential mechanisms.The proliferation of SGC7901 cells was monitored by the MTT cell viability assay,while the nuclear morphology of apoptotic cells was assessed by Hoechst 33258 staining.Flow cytometry was performed to analyze the cell cycle progression of propidium iodide (PI)-stained SGC7901 cells and the apoptotic rate of annexin V/PI-stained cells.Western blotting was used to examine the expression of several cell cycle proteins,including cyclin B1 and Cdkl,and the apoptosis-regulated proteins Bcl-2,Bax,cytochrome c,procaspase-9,and procaspase-3.The MTT assay demonstrated that PSⅠ could induce significant doseand time-dependent inhibition of SGC7901 cell proliferation.Marked morphological changes,including condensation of chromatin,nuclear fragmentation and apoptotic bodies were clearly shown on Hoechst 33258 staining.PSⅠ treatment also resulted in the disruption of the cell cycle at G2/M and the induction of apoptosis.Following PSⅠ treatment,the cell cycle-related proteins cyclin B 1 and Cdk1 were downregulated.Expression of the pro-apoptotic protein Bax was increased,while anti-apoptotic protein Bcl-2decreased.PSⅠ treatment resulted in elevated cytoplasmic cytochrome c and activation of the apoptotic proteases caspase-9 and caspase-3.These data indicate that PSⅠ acts as an inhibitor of proliferation in SGC7901 cells by inducing cell cycle arrest and mitochondria-dependent apoptosis.PSⅠ is a potential therapeutic agent against human gastric carcinoma.