Urchinlike NiO nanostructures were prepared by thermal decomposition of the precursor obtained via a hydrothermal process using urea as a hydrolysis-controlling agent and polyethylene glycol (PEG) as a surfactant. The structure and morphology of the samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared absorption spectra (IR). Structure characterizations indicated urchinlike nanostructures for the nickel oxide samples with high purity. Electrochemical properties of urchinlike NiO were examined by cyclic voltammetry and galvanostatic charge-discharge measurements. The results showed that NiO calcined at 300 degrees C had a higher specific capacitance and better capacitive behavior than NiO calcined at 500 degrees C. The specific capacitance of about 290 and 170 F g(-1), respectively, could be achieved with NiO calcined at 300 and 500 degrees C in the voltage range of 0.0-0.5 V. The calculated capacitances decreased with the increase of cycle number of the NiO sample. The specific capacitance of NiO calcined at 300 degrees C decreased to 217 F g(-1) after 500 cycles. It revealed that the NiO materials exhibited good cycling performance. NiO calcined at 300 degrees C possessed the high capacitance because it had the high surface redox reactivity due to its special nnostructures. (c) 2005 Elsevier Ltd. All rights reserved.