Objective To investigate the effect of Arsenic Trioxide(As_2O_3) combined with radiation on the apoptosis of nasopharyngeal carcinoma cells in vitro.Methods Using MTT and FCM to detect the cytotoxic and apoptosis at different As_2O_3 concentrations combined with 2Gy radiation on nasopharyngeal carcinoma cells(CNE1).Results Inhibition of cell proliferation seemed more dependent on the increase of As_2O_3 concentration.Cell survival rate was lower in the combination of As_2O_3 and radiation group than As_2O_3 alone.Conclusion As_2O_3 can enhance radiation effect obviously in nasopharyngeal carcinoma cells,especially at lower radiation dose.