Hydrothermal synthesis has been introduced to fabricate NiO precursor at different temperatures. then nanostructured NiO with a distinct flake-like morphology was obtained via heating at low temperature. The NiO nanoflakes are 50-80 nm in width and 20 nm in thickness. The electrochemical capacitive characterization of the as-prepared NiO was studied in 2 M KOH electrolyte solution, The as-prepared NiO exhibits excellent cycle performance and keeps 91.6% initial capacity over 1000 charge-discharge cycles. Electrochemical impedance spectroscopy study reveals that the NiO electrode is controlled by the mass transfer limitation, and its internal resistance is 0.2 Omega. A specific capacitance approximate to 137.7 F g(-1) could be achieved at the current density of 0.2 A g(-1) in the potential window of 0-0.46 V in 2 M KOH electrolyte solution, due to higher surface area of NiO nanoflakes, which facilitates transport or electrolyte ions during rapid charge/discharge process. Due to higher Surface area of NiO nanoflakes, which facilitates transport of electrolyte ions during rapid charge/discharge process. (C) 2008 Elsevier Ltd. All rights reserved.