To investigate the mechanism of arsenic trioxide (As2O3)-induced apoptosis of glioma cells.U87 cells were treated by different concentrations of As2O3 (8 μmol/L, 6 μmol/L, 4 μmol/L, 2 μmol/L, 1 μmol/L and 0.5 μmol/L) for 24 h, 48 h and 72 h, respectively. Cell viability was detected by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and the appropriate dosage and time were screened. Transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) was used to stain cells, followed by an investigation on the apoptosis of cells. In the study of molecular mechanism, the expression of p53 in the cells was determined by immunofluorescence, and then apoptosis-related factors, Fas, FasL and Bax, were tested using Real-time polymerase chain reaction (RT-PCR). Finally, the effect of As2O3 on apoptosis-related proteins, caspase-3 and caspase-9, was investigated by Western blotting.As2O3 could significantly inhibit proliferation of U87 cells, and the result of TUNEL staining displayed As2O3 had the function of inducing apoptosis. Immunofluorescence results demonstrated that p53 was highly expressed in glioma cells, which was reduced after drug administration. The results of detection of apoptosis factors using RT-PCR revealed that mRNA expressions of Fas, FasL and Bax in the glioma cells were distinctly higher than those in the As2O3 group. The result of Western blotting indicated that caspase-3 and caspase-9 proteins were highly expressed in glioma cells. Analysis of variance showed that the difference between the control group and the As2O3 group was statistically significant (p<0.01).As2O3 can inhibit proliferation of glioma cells and induce its apoptosis, which may be correlated with down-regulation of expressions of apoptosis-related factors, Fas, FasL and Bax, and apoptosis-related proteins, p53, caspase-3 and caspase-9.