Ruthenium oxide was electrochemically prepared onto a carbon nanotube (CNT) film substrate with a three-dimensional nanoporous structure in order to improve the specific capacitance and high-rate capability of ruthenium oxide, a promising electroactive material for supercapacitors. A very thin and uniform deposition of ruthenium oxide on the CNT film substrate was obtained by the potential cycling method. Electrochemical properties such as the specific capacitance and high-rate capability were studied by cyclic voltammetry. The electrochemically prepared ruthenium oxide onto the CNT film substrate showed both a very high specific capacitance of 1170 F/g and a high rate capability. (c) 2005 The Electrochemical Society.