Ultrafine ruthenium-vanadate particles possessing a rutile-type structure, Ru1-xVxO2, were prepared by a polymerizable-complex method and their electrochemical supercapacitor behavior was studied by cyclic voltammetry in an acidic solution. The solid solution exhibited enhanced supercapacitive properties compared to pure RuO2. The present electrode material possessed excellent cyclability and specific capacitance. Specific capacitance exceeding 1200 F g(-1) of RuO2 was obtained for Ru0.35V0.65O2. (C) 2002 The Electrochemical Society.