Abstract: Objective To investigate the role of specificity protein 1 (Sp1) in regulating radiosensitivity of cervical cancer cell lines. Methods We analyzed Sp1 expression in 6 different cervical cancer cell lines (SiHa, HeLa, Caski, Me180, Ms751, and C33a) using Western blotting and real-time PCR. Clonogenic survival assay and curve fitting were used to assess the changes in radiosensitivity of Me180 cells transfected with lentivirus-mediated shRNA vector targeting sp1 and HeLa cells transfected with sp1 over-expression vector. Results In the 6 cell lines tested, the cellular expression levels of Sp1 decreased gradually in the order of Me180, Caski, C33a, SiHa, Ms751, and HeLa. SP1 knockdown with lentivirus-mediated shRNA significantly lowered the survival rate of Me180 cells following radiation exposure (P<0.05), and obviously lowered the values of SF2, D0 and Dq but significantly increased α/β of the cells. Compared with the cells transfected with the mock vector, HeLa cells with sp1 over-expression showed a significantly increased survival following radiation exposure (P<0.05) with obviously increased values of SF2, D0 and Dq but significantly lowered α/β. Conclusion Silencing Sp1 can increase the radiosensitivity while Sp1 overexpression enhances the radioresistance of cervical cancer cell lines, suggesting an important role of Sp1 in radiotherapy for cervical cancer.