Metallic Cobalt nanoparticles segregated in situ on conductive vanadium nitride (Co/VN) nanosheets synthesized by ammonia nitridation of hydrothermally prepared Co2V2O7 nanosheets are investigated as high-performance oxygen evolution reaction (OER) electrocatalysts. The metallic Co nanoparticles with a large number of exposed active sites are distributed uniformly and adhere firmly to the VN substrate to enhance the OER efficiency, facilitate fast charge transfer, and improve the stability. As a result, a small overpotential of 320mV is required to achieve a current density of 10mAcm−2 with a small Tafel slope of 55mVdec−1. The excellent stability is indicated by an overpotential shift of only 34mV after 2000 cyclic voltammetry cycles at a large current density of 200mAcm−2. The precious-metal-free Co/VN nanosheets deliver outstanding OER performance and are promising as electrocatalysts in water splitting and related applications.