Electrocatalytic N2 fixation has been considered a most promising approach for sustainably producing NH3 under ambient conditions. However, owing to the strong chemical inertness of N2, it is highly desired to explore efficient electrocatalysts for improving the yield and selectivity of nitrogen reduction. Herein, CeO2 and Mo2C nanoparticles embedded simultaneously in reduced graphene oxide nanosheets (CeO2/Mo2C@rGO) are successfully fabricated for catalyzing N2 fixation. The as-obtained CeO2/Mo2C@rGO catalyst shows superior catalytic performance with an NH3 yield of 22.3 μg h-1 mg-1 and a faradaic efficiency (FE) of 12.7% at -0.3 V vs. the RHE, distinctly outperforming the undoped Ce counterpart of Mo2C@rGO. The experimental and DFT calculations reveal that the introduced Ce optimized the electronic structure, contributing to the improved NRR performance.