We report successfully synthesizing two-dimensional (2D) and nanocrystalline (NC) Fe2Ni2N/rGO nanohybrid sheets (NHSs) via ammonolysis of as-prepared 2D Ni2.25Fe0.75[Fe(CN)6]2/rGO precursors. We compared the electrochemical properties of the 2D-NC Fe2Ni2N/rGO NHSs as non-precious-metal nitride and graphene nanohybrid electrocatalysts for an oxygen evolution reaction (OER) with those of NiFe-based composition. The overpotential and Tafel plot of the 2D-NC Fe2Ni2N/rGO NHSs had their lowest values of 290 and 49.1 mV dec-1, respectively, at a current density of 10 mA cm-2 (0.1 M, KOH). The 2D-NC Fe2Ni2N/rGO NHS catalyst was stable under OER conditions, and X-ray photoelectron spectroscopy and scanning transmission electron microscopy confirmed the stability of the catalysts after electrochemical testing (24 h). The synergistic interactions between the transition-metal nitride and graphene represent unique 2D nanostructured, metallic properties, and graphene sheets with nanocrystalline Fe2Ni2N on them are significantly more efficient and active electrocatalysts. The presented strategy of transition-metal nitride/graphene hybrid nanostructures provides potential for more efficient and outstanding OER electrocatalysts.