Nanosized nickel oxide powders were prepared by thermal decomposition of the nickel citrate gel precursors. The thermal decomposition and powder materials derived from calcination of these gel precursors with various ratios of citric acid (CA) to nickel at different temperatures and times were characterized by thermal analysis (TG/DTA), scanning electron microscopy (SEM), x-ray diffraction (XRD), and measurement of specific surface area (BET) with porosity analyses. The optimized processing conditions of calcination temperature 400℃ for 1 hour with the CA/Ni ratio of 1.2,were determined to produce the nanosized nickel oxide powders with a high specific surface area of 181 m2/g,nanometer particle sizes of 15-25 nm,micro-pore diameter distribution between 4-10 nm.The capacitance characteristics of the nanosized nickel oxide electrode in various concentrations of KOH solutions were studied by the cyclic voltammetry (CV) exhibiting both a double-layer capacitance and a faradaic pseudocapacitance.The nanosized nickel oxide electrode shows a high cyclic stability and is promising for high performance electrochemical capacitors.