Abstract: Objective To investigate the effects of miR-3942-3p on the radiosensitivity of endometrial carcinoma cells and its possible mechanism. Methods The levels of miR-3942-3p and BRCA1 associated RING domain 1 (BARD1) in human endometrial cancer -1A (HEC-1A) cells and human endometrial epithelial cells(HEECs) were detected by quantitative real-time PCR (RT-qPCR). HEC-1A cells were irradiated with 0, 2, 4 and 6 Gy of X-rays. The amounts of miR-3942-3p and BARD1 were detected by RT-qPCR.After down-regulating the expression of miR-3942-3p and 6 Gy X-ray irradiation, the proliferation and apoptosis of HEC-1A cells were detected by CCK-8 assay and flow cytometry, respectively; while the amounts of B-cell lymphoma-2 (Bcl-2) and BCL2-associated X (Bax) in HEC-1A cells were measured by Western blot. The relationship between miR-3942-3p and BARD1 was analyzed by Targetscan and dual luciferin reporter assay. After down-regulating BARD1 expression and 6 Gy X ray irradiation, the proliferation and apoptosis of HEC-1A cells were detected by CCK-8 assay and flow cytometry, respectively, while the amounts of Bcl-2 and Bax in HEC-1A cells were measured by Western blot. The effects of miR-3942-3p via BARD1 on the radiosensitivity of HEC-1A cells were detected. Results Compared with those in adjacent non-cancer tissues, the levels of miR-3942-3p in endometrial carcinoma tissues significantly decreased (P<0.05),but the amounts of BARD1 significantly increased (P<0.05). Compared with HEEC cells, the levels of miR-3942-3p in HEC-1A cells significantly decreased (P<0.01), but the amounts of BARD1 significantly increased (P<0.01). The expression of miR-3942-3p increased after radiation in a dose-dependent manner. The expression of BARD1 decreased after radiation in a dose-dependent manner. After 6 Gy X-ray irradiation,down-regulation of miR-3942-3p reduced the radiosensitivity of HEC-1A cells. MiR-3942-3p targeted on BARD1. After downregulation of BARD1, 6 Gy X-ray irradiation increased the proliferation abilities of HEC-1A cells and reduced the apoptotic rate. Upregulation of miR-3942-3p enhanced the radiosensitivity of HEC-1A cells via BARD1. Conclusions Up-regulation of miR-3942-3p negatively targets BARD1 and enhance the radiosensitivity of endometrial carcinoma cells.