Objective To investigate the inhibitory effects ofPolyphyllin D (Paris saponin [PS]Ⅰ) and formosanin C (PS Ⅱ) on human glioblastoma U251 cells and its mechanism.Methods Glioma cell line U251 was cultured in vitro.Different treatments (PSⅠ and PS Ⅱ) were added into the medium cultured human malignant glioma U251 cells; and blank control group was also established.The effects of PSⅠ and PS Ⅱ on proliferation of glioma cells U251 in vitro was examined using methyl thiazolyl tetrazolium (MTT) assay.The nuclear morphology changes of apoptotic cells were detected by Hoechst33258 fluorescent staining.Apoptotic rate was quantified by flow cytometry (FCM) using Annexin-V/PⅠ dual staining.Western blotting was used to evaluate the changes of Fas,Caspase-8 and Caspase-3 proteins in U251 cells.Results PS Ⅰ and PS Ⅱ inhibted U251 cell proliferation with a timeand dose-dependent manner; as compared with that in the blank control group,the proliferation rate in the PSⅠ and PS Ⅱ treatment groups was significantly increased (P＜0.05); PS Ⅰ had stronger inhibited effect than PS Ⅱ.Typical morphological changes of apoptosis were observed in U251 cells of the PSⅠ and PS Ⅱ treatment groups with Hoechst 33258 staining.The early apoptotic rates of the PSⅠ and PS Ⅱ treatment groups were all significantly higher than that of the blank control groups (F=81.434,P=0.000).As compared with those in the blank control group,the expressions ofFas,Caspase-8 and Caspase-3 were significantly increased (P＜0.05).Conclusion PSⅠ and PS Ⅱ inhibite the proliferation ofglioma cells in vitro; they increase the expressions ofFas,Caspase-8 and Caspase-3,and accelerate the cell apoptosis,which might be the mechanism of inhibition.