Amorphous tungsten oxide/ruthenium oxide composites have been synthesized by precipitating amorphous RuO2. xH(2)O on amorphous WO3. xH(2)O and Na0.37WO3. xH(2)O under various pH conditions. The samples have been characterized by X-ray powder diffraction, elemental analysis using wavelength dispersive spectroscopy (WDS), thermogravimetric analysis, and surface area measurements. The compositions and electrochemical performance of the products are influenced by the precipitation reaction pH. The amorphous, as-prepared samples transform to rutile-type phases on heating at T greater than or equal to 400 degreesC. Amorphous samples with tungsten content as high as 50 wt % exhibit specific capacitance values of around 560 F/g, which is 200 F/g higher than that expected on the basis of rule of mixture, and thus lower the cost per unit capacitance considerably. (C) 2001 The Electrochemical Society. All rights reserved.