Objective:To study the radiosensitivity of SiHa cells with Ku80 inhibition by RNAi.Methods:pKu80-siRNA and pNeg-siRNA were constructed and then transfected into SiHa cells.Western blot and RT-PCR were applied to measure the expression of Ku80.After 10 Gy irradiation with 6 MV X-ray,cells were harvested at 20 h,28 h and 48 h,and analyzed by flow cytometry for apoptosis rate.The SF2 and α,β values of cells were acquired by clone formation array.Results:Two stable transfection cell clones SiHa/Ku80-siRNA and SiHa/Neg-siRNA were screened from the pKu80-siRNA and pNeg-siRNA transfected cells.Western blot and RT-PCR indicated that the expression of Ku80 was suppressed by fhe Ku80-siRNA.The apoptosis rates of SiHa/Ku80-siRNA were higher than control cells at 28 h and 48 h after X-ray irradiation (P＜0.05).The SF2 value of SiHa/Ku80-siRNA(0.422)was fower than that of SiHa/Neg-siRNA cells(0.587)or untransfected cells(O.583),and theαvalue of SiHa/Ku80-siRNAwas 0.295±0.016,higher than that of SiHa/Neg-siRNA (0.176±0.010)or control cells (0.188±0.011).Conclusion:Inhibition of Ku80 could enhance the radiosensitivity of SiHa,which showed that Ku80 could be a good target for molecular therapy.