Objective To investigate the effect of circ_NEK6 on the malignant biological behavior of 131I⁃ resistant differentiated thyroid carcinoma （DTC）cells and its possible mechanism. Methods RT ⁃ qPCR was performed for the detection of circ_NEK6 and miR⁃370⁃3p in DTC tissues and cell lines. The proliferation，apoptosis， migration and invasion abilities of Res⁃BCPAP cells was evaluated by CCK⁃8，flow cytometry，Transwell assay， respectively. Dual⁃luciferase assay was conducted to prove the interaction of circ_NEK6 and miR⁃370⁃3p. Results circ_NEK6 was upregulated in the 131I⁃resistant DTC tissues compared with the 131I⁃sensitive DTC tissues，and its expression in DTC cell lines was higher than that in human thyroid follicular epithelial normal cells，especially in 131I⁃resistant Res⁃BCPAP cells was higher than that in parental BCPAP cells. Knockdown of circ_NEK6 decreased Res⁃BCPAP cell proliferation，migration and invasion，as well as promoted cell apoptosis. Besides，dual⁃luciferase reporter gene assay analysis results showed that circ_NEK6 could directly bind to and negatively regulate miR⁃370⁃ 3p expression. Functionally，circ_NEK6 suppression inhibited the malignant biological behavior of Res ⁃ BCPAP cells via targeting miR⁃370⁃3p. Conclusion Inhibition of circ_NEK6 enhanced the radio⁃sensitivity of 131I in DTC cells via targeting miR⁃370⁃3p，indicating that circ_NEK6 may act as a potential biomarker and therapeutic target for DTC patients with 131