Objective To study the effect of arsenic trioxide(As 2O 3) combin ed w ith radiation on the killing of ovarian cancer cells. Methods Using MTT and FCM to detect the cytotoxic and apoptosis at different As 2O 3 concentrations combined with 2 an d 8 ?Gy radiation on ovarian cancer cells(SKOV-3). Radiation survival curves were det ermined by cloning assay with 5?mol/L As 2O 3 combined with 2, 3, 4, 6, 8 and 12?Gy radiation. Curve was used to evaluate the effect of cell killing. Results ⑴ Inhibition of cell proliferation seemed more dependent on the increase of As 2O 3 concentration, ⑵Cell survival rate was lower in the combination of As 2O 3 an d r adiation than As 2O 3 alone, ⑶The apoptosis ratio was increased in 2?Gy and As 2O 3 with increase in As 2O 3 concentration, ⑷D q , D 2 value was decr eased in t he combined As 2O 3 and radiation than radiation only (D q: 1.44 vs 2.78, D 0: 0.85 vs 1.30, SF 2: 0.42 vs 0.87), with radiation enhancement ratio of 1.53 and 2.0 7 according to D 0 value and SF 2. Conclusions Arsenic trioxide is able to enhanc e radiation effect obviously ,especially at lower radiation dose.