Resistance to radiotherapy accounts for most therapeutic failures in cervical cancer patients who undergo radical radiation therapy. To indicate the possible molecular mechanism of radioresistance and improve the 5-year survival rate, we focused on how SET domain protein 3 (SETD3) regulated radioresistance in human cervical cancer cells in this study. Our results indicated that SETD3 over-expression markedly increased the radiosensitivity of cervical cancer cells with radioresistance, as evidenced by the further reduced cell viability, proliferation, DNA damage and cell death. In addition, we found that SETD3 down-regulated the expression of kinesin light chain 4 (KLC4), contributing to the radiosensitivity of cervical cancer cells, and the regulatory role of SETD3 could be abolished by KLC4 over-expression. Moreover, nitric oxide (NO) production was significantly reduced by SETD3 over-expression through repressing the expression of inducible NO synthase (iNOS) and endothelial NO synthase (eNOS) in cervical cancer cells. In vivo studies using xenograft animal models also demonstrated that SETD3 over-expression combined with irradiation treatment markedly inhibited tumor growth and induced apoptosis. In summary, our data demonstrated that down-regulated SETD3 expression markedly led to the progression of radioresistance and that promoting SETD3 expression could sensitized cervical cancer cells to radiotherapy, thereby targeting SETD3 might be a potential strategy for the clinical management of cervical cancer to improve the curative effect of radiation in cervical cancer.