Preparation of RuOxHy/carbon black nanocomposite material was performed by the impregnation method starting from RuOxHy sol as a precursor. Black Pearls 2000(R) (BP) and Vulcan(R) XC-72 R (XC) were used as supporting materials. Samples of the composite were calcined in nitrogen atmosphere at temperatures from 130 to 450 degreesC. Chemical and structural characterization of the precursor and the composites was performed by using energy-dispersive X-ray fluorescence spectroscopy (EDXRFS), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). These techniques showed that the oxide impregnated into carbon support is hydrous and amorphous. The amorphous structure is maintained if the composite is calcined up to 300 degreesC, while the lowintensity peak at 2theta position that corresponds to the most intensive peak of the rutile structure was registered at 450 degreesC. The capacitance of the composite was determined using cyclic voltammetry. It was found that the capacitance is dependent on calcination temperature and surface area of the carbon black support. The highest specific capacitance of about 700 F g(-1) of composite was registered for RuOxHy supported on BP and calcined at 300 degreesC while four times lower values was obtained for RuOxHy supported on XC. The capacitance measurements indicated that XC-supported RuOXHy composite is highly porous while BP-supported one is more compact. (C) 2003 Elsevier Ltd. All rights reserved.