Three radioresistant cervical cancer cell variants were established. The radioresistant variants Hela-R11 (A) and Siha-R15 (B) were established by exposing Hela and Siha cells to 11 and 15 cycles of sequential radiation, respectively. Another radioresistant cervical cancer cells Hela-NDRG2 (C) and their control Hela-C cells were generated in our previous study by transfection with constructs expressing NDRG2 and control vector respectively in Hela cells. The cervical cancer cells were exposed to irradiation at indicated dosage and survival fractions were determined by colony-forming assay as described in “Materials and methods”. Data was expressed as mean ± SD of triplicates in one experiment. Shown was representative of at least 3 experiments.