The suitable materials, metal nitrides, are a promising class of electrocatalyst materials for a highly efficient oxygen evolution reaction (OER) because they exhibit superior intrinsic conductivity and have higher sustainability than oxide-based materials. To our knowledge, for the first time, we report a designable synthesis of three-dimensional (3D) and mesoporous Co₃N@amorphous N-doped carbon (AN-C) nanocubes (NCs) with well-controlled open-framework structures via monodispersed Co₃[Co(CN)₆]₂ Prussian blue analogue (PBA) NC precursors using in situ nitridation and calcination processes. Co₃N@AN-C NCs (2 h) demonstrate better OER activity with a remarkably low Tafel plot (69.6 mV∙dec^-1), low overpotential of 280 mV at a current density of 10 mA∙cm^-2. Additionally, excellent cycling stability in alkaline electrolytes was exhibited without morphological changes and voltage elevations, superior to most reported hierarchical structures of transition-metal nitride particles. The presented strategy for synergy effects of metal-organic frameworks (MOFs)-derived transition-metal nitrides-carbon hybrid nanostructures provides prospects for developing high-performance and advanced electrocatalyst materials.