CuBi O hierarchical microspheres are synthesized via a coprecipitation method, where the effect of the NaOH concentration in precursor solution on the product morphology is investigated. At n(NaOH) = 1 M, irregular microspheres of 0.5-1 μm are produced. With increase in the concentration of NaOH, the microspheres grow bigger in size and more regular in morphology. When the NaOH concentration is increased up to 6 M, regular microspheres of 4-6 μm in diameter are obtained. These microspheres are constructed from nanorods with 30-60 nm in diameter and 200-400 nm in length via the hierarchical self-assembly process. The electrochemical performances of the as-prepared samples are investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge. It is demonstrated that the sample composed of 0.5-1 μm microspheres exhibits the highest specific capacity, reaching about 1895 F g in a 2 M KOH electrolyte at a measured current density of 1 A g . This value is larger than the specific capacity for most transition metal oxides. Due to its excellent electrochemical performance, CuBi O could find a promising application as the supercapacitor electrode material. 2 4 2 4 -1 -1