Highly efficient electrocatalysts for oxygen evolution reaction play key roles in various energy storage/conversion devices. Promoting the reaction rates and decreasing the overpotentials of the electrocatalysts for oxygen evolution reaction are critical for their practical application. Herein, we realize the first successful synthesis of Co2N0.67 with three-dimensional architecture of hierarchical meso-macroporous nanoflowers stacked by the nanoplates with polystyrene spheres as the template. The Co2N0.67 nanoflowers exhibit both low overpotential (258 mV at 10 mA cm−2) and low Tafel slope (52.22 mV dec−1) as well as superior stability for oxygen evolution reaction in alkaline medium, which makes Co2N0.67 nanoflowers to be one of best earth-abundant elements based electrocatalysts toward oxygen evolution reaction to date. Importantly, being different from the previous observation that the cobalt nitrides with higher nitrogen content possess lower oxygen evolution reaction electrocatalytic abilities, we find Co2N0.67 exhibits higher oxygen evolution reaction activity than Co5.47N. The density functional theory calculations reveal that during the oxygen evolution reaction, the oxidation step from O* to OOH* on Co2N0.67 and Co5.47N is considered as the rate-determining step, making oxygen evolution reaction to be more thermodynamically favorable on Co2N0.67 than that on Co5.47N.