Capsule-like NiO nanoparticles were prepared by heat-treatment of the cathodically electrodeposited nickel hydroxide at 300 degrees C for three hours. The hydroxide precursor was deposited galvanostatically onto the stainless steel substrate from aqueous Ni(NO3)(2) solution (0.01 M). Morphological, structural and chemical characteristics of the synthesized NiO were examined by means of scanning and transmission electron microscopy (SEM and TEM) as well as X-ray diffraction (XRD) and FT-IR spectroscopy. The XRD and TEM results revealed that the oxide products have well-crystallized cubic structure with capsule-like morphology of various length and diameters in the order of 20-70 nm and 10-30 nm, respectively. Capacitive performance of NiO nanocapsules were evaluated by cyclic voltammetry and galvanostatic charge/discharge measurements in a potential window between -0.2 and +0.5 V vs. Ag/AgCl. Electrochemical measurements revealed that the NiO nanocapsules have a specific faradaic pseudocapacitance as high as 307.2 F g(-1) in 1 M KOH solution and good cycle life (approximately displayed 86.4% of its maximum capacitance after 3000 cycle discharging). These results showed that the prepared NiO nanostructure can be recognized as a promising candidate for the supercapacitor applications. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.106206jes] All rights reserved.