NiO x xerogels were formed by the sol–gel method followed by heat-treatment under ambient pressure. The structure and properties of these materials were characterized by using X-ray diffraction, XPS, TEM, TGA–DTA and N2 (77K) adsorption. Electrodes with the xerogels were activated by cyclic voltammetry (CV) and their capacitive performance was evaluated by CV and galvanostatic technique in 7M KOH solutions. A maximum specific capacitance of 696Fg−1 was obtained by constant current discharge with a current density of 2.0mAcm−2 for the NiO x xerogels heat-treated at 250°C. The results of in situ XRD of the NiO x xerogels after the charge/discharge recycling test showed that the NiO x xerogels might exhibit faradaic pseudocapacitance by surface redox from Ni(OH)2 to NiOOH. The high performance obtained indicates that these materials are promising electrode materials for supercapacitors.