Vertical copper oxide (CuO) nanoflakes have been formed by oxidation in NaOH solution. Their structural, surface morphology and oxidation states were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) respectively. Pseudocapacitive behavior of CuO nanoflakes was investigated by cyclic voltammetry and constant current charge-discharge test. CuO nanoflakes were vertically grown with high lateral aspect ratio and consist of monoclinic lattice as shown by the presence of two peaks close to 20 = 35.6 degrees and 38.7 degrees in the XRD. Charge-discharge test gave a capacitance value of 190 F g(-1) in 1.0 M KOH electrolyte at 2 mA cm(-2) current density. The cycling test showed 67% stability after 2000 cycles and reduced specific capacitance from 190 F g(-1) to 125 F g(-1). Specific capacitance of CuO nanoflakes is higher than 26.44 F g(-1) of globular CuO at 2 mA cm(-2) as reported in literature due to enhanced specific surface area. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.