Ruthenium oxide-carbon composites with different loadings of RuO2 on carbon have been synthesized by an electroless deposition process. Increase in RuO2 loading results in increasing the specific capacitance of the composite electrode. The effect of temperature treatment on the performance of these materials has been studied in detail. Maximum capacitance was observed after heat treatment at 100 degreesC for all the composites. Increasing the oxidation temperature further converts the Ru oxides to crystalline form, which leads to poor capacitance values. ii maximum capacitance of 260 F/g was obtained for 20 wt.% RuO2 loaded carbon treated at 100 degreesC. The volumetric surface area of the composite remains constant with increased RuO2 loading. Since Ru oxides have a large pseudocapacitance, this increases the volumetric capacitance of the carbon significantly. (C) 2001 Elsevier Science B.V. All rights reserved.