The thin films of carambola-like γ-MnO2 nanoflakes with about 20nm in thickness and at least 200nm in width were prepared on nickel sheets by combination of potentiostatic and cyclic voltammetric electrodeposition techniques. The as-prepared MnO2 nanomaterials, which were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were used as the active material of the positive electrode for primary alkaline Zn/MnO2 batteries and electrochemical supercapacitors. Electrochemical measurements showed that the MnO2 nanoflake films displayed high potential plateau (around 1.0V versus Zn) in primary Zn/MnO2 batteries at the discharge current density of 500mAg−1 and high specific capacitance of 240Fg−1 at the current density of 1mAcm−2. This indicated the potential application of carambola-like γ-MnO2 nanoflakes in high-power batteries and electrochemical supercapacitors. The growth process for the one- and three-dimensional nanostructured MnO2 was discussed on the basis of potentiostatic and cyclic voltammetric techniques. The present synthesis method can be extended to the preparation of other nanostructured metal-oxide films.