Evidence has demonstrated that microRNAs (miRNAs) are important in the regulation of cellular radiosensitivity of various types of human cancer. The aim of this study was to examine the role of miR-18a in regulating the radiosensitivity of cervical cancer, in order to understand the underlying mechanism and to assess the potential of miR-18a as a biomarker for predicting radiosensitivity. The expression of miR-18a was investigated in 48 cervical cancer patients. The results revealed that miR-18a expression was significantly higher in radiosensitive patients than in radioresistant patients by RT-qPCR (P<0.05). Transient transfection experiments showed that miR-18a was upregulated by the miR-18a mimic and downregulated by the miR-18a inhibitor in the SiHa and HeLa cells. Without irradiation treatment, a similar growth was observed in the cells with or without transfection of miR-18a. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and Hoechst staining assays showed that miR-18a had no effect on the proliferation and apoptosis of cervical cancer cells after transfection. However, the upregulation of miR-18a suppressed the level of ataxia-telangiectasia mutated and attenuated DNA double-strand break repair after irradiation, which re-sensitized the cervical cancer cells to radiotherapy by promoting apoptosis. Taken together, these results demonstrated that miR-18a is a potential molecule predictor of radiosensitivity in cervical cancer patients and played an important role in the response to radiotherapy.