A facile method to synthesize hierarchical architectures of Co₃O₄ nanowires@Co₃O₄ ultrafine nanowires grown on Ni foam was developed here. The unique architectures consisting of numerous ultrafine Co₃O₄ nanowires (shell) well grown on the surface of a Co₃O₄ nanowire (core) delivered remarkable electrochemical performance with ultrahigh specific capacitance (1640 F g⁻¹ at a current density of 2 mA cm⁻²), superior rate capability (66% retention of the initial capacitance from 2 mA cm⁻² to 50 mA cm⁻²) and outstanding cycling stability (∼99.03% retention of the initial capacitance after 10 000 cycles). Such fascinating capacitive behaviors can make these hierarchical architectures of Co₃O₄ nanowires@Co₃O₄ ultrafine nanowires promising electrode materials in electrochemical applications.