Objective To investigate the role and mechanism of miR-10b-5p in radiosensitivity of breast cancer cells.Methods The expressions of SUFU mRNA, SUFU protein and miR-10b-5p in normal breast cells MCF-10A and breast cancer cells MCF-7, SKBR-3 and MDA-MB-231 were detected by qPCR and Western blotting. miR-10b-5p in MDA-MB-231 cells was knocked down by transfected with miR-10b-5p inhibitor, and then treated with 6 Gy ⁶⁰Co γ-ray for 2 h. Cell proliferation and apoptosis levels were detected respectively by clone formation assay and flow cytometry. The dual luciferase reporter assay was used to validate the target gene SUFU, and the remediation experiment was performed to verify whether miR-10b-5p mediated the sensitivity of breast cancer cells to radiotherapy by targeting SUFU.Results The expression of miR-10b-5p in the three breast cancer cell lines was significantly higher than in the normal breast cells (P<0.05). Compared with the miR-NC group, the cell proliferation of miR-10b-5p inhibitor group was decreased significantly (P<0.05), and the cell apoptosis rate was significantly increased in miR-10b-5p inhibitor group (P<0.05). The dual luciferase report showed that miR-10b-5p knockdown increased the fluorescence intensity of the wild-type SUFU 3'UTR, but had no effect on the fluorescence intensity of the mutant SUFU 3'UTR. In addition, the SUFU protein expression of miR-10b-5p inhibitor group was significantly higher than that of miR-NC group, with statistically significant difference (P<0.05). Compared with miR-NC+si-NC group, the cell proliferation level was significantly decreased in miR-10b-5p inhibitor+si-NC group (P<0.05), while it was significantly increased in miR-10b-5p inhibitor+si-SUFU#2 group, which was also higher than in miR-10b-5p inhibitor+ si-NC group (P<0.05).Conclusion miR-10b-5p is highly expressed in breast cancer cells. Knockdown of miR-10b-5p can enhance the sensitivity of breast cancer cells to radiotherapy, and the mechanism may be related to the targeted inhibition of SUFU.