Nasopharyngeal carcinoma (NPC) has high incidence in China and East and Southeast Asia. The study was performed to investigate the effect of microRNA3942-3p (miR-3942-3p) on the radiosensitivity of NPC. Compared with non-cancer tissue, NPC had significantly lower miR-3942-3p expression. X-irradiation (IR) reduced the expression of miR-3942-3p in a dose-dependent way in NPC cells. Down-regulation of miR-3942-3p using miR-3942-3p inhibitor resulted in significantly increased cell viability, decreased apoptosis of CNE1 cells. Bax decreased and Bcl2 increased after IR. The expression of BARD1, a cancer predisposing gene, was elevated in NPC tissue. It was confirmed to be a target of miR-3942-3p using luciferase reporter assay. Down-regulation of BARD1 using siRNA significantly reduced cell viability and significantly increased apoptosis both before and after IR. The same response was observed when miR-3942-3p mimics was used to transfect BARD1-overexpressing CNE1 cells, suggesting the up-regulation of miR-3942-3p could sensitize CNE1 cells to X-rays via BARD1. Our data demonstrate that up-regulation of miR-3942-3p could sensitize NPC to X-rays via a downstream target BARD1, offering potential new strategies for radiotherapy of NPC.