Objective To investigate the effects of titanium dioxide ( TiO2 ) nanoparticles coupled with nuclear localization sequence ( NLS ) on the radiosensitivity of U251 glioma cells. Methods Synthesis and characterization of the TiO2-NLS nanoparticles with nuclear targeting property. U251 cells were treated with nanoparticles and/or ionizing radiation. Flow cytometry analysis was performed to measure the ROS content and the cell apoptotic percentage. The DNA damage was detected by using γ-H2AX foci staining. Clonogenic survival assay was used to evaluate the radiosensitivity of U251 cells. Results NLS modification promoted nuclear translocation of TiO2 nanoparticles. Compared with the control nanoparticles, TiO2-NLS treatment increased radiation-induced cell apoptosis (t=8. 96, P<0. 05). Clonogenic survival assay showed the radiosensitization ratios of TiO2 nanoparticle-treated group and TiO2-NLSnanoparticle-treated group were 1. 18 and was 1. 29, respectively. These two ratios had statistically difference ( t =14. 72, P< 0. 05). Conclusions Nuclear targeting TiO2 nanoparticles enhances the radiosensitivity of U251 glioma cells.