Electrodes of hydrous ruthenium oxide were prepared by electrophoretic deposition (EPD) without binder and carbon additives. Through EPD and heat-treatment (250 degrees C), a network of nanoparticles (ca. 10 nm) was developed with porous structure packing density ca. 1.9 g/cm(3)). As a result, high specific capacitance (734 F/g at 1 mV/s and 608 F/g at 50 mV/s) was obtained, where specific energy and power were as high as 25 Wh/kg (at 92 W/kg) and 21 kW/kg (at 12 Wh/ kg), with loading weight of 0.19 mg/cm(2). At higher loading weight (> 0.4 mg/cm(2)), specific capacitance decreased gradually. Also, volumetric energy was high because low-density additives, such as porous carbon and binder, were not used. From electrochemical impedance spectroscopy, specific energy and power were calculated, showing good agreement with values measured by CV. The decrease of rate capability with thicker electrode could be correlated by distribution of the time constant (tau), which was calculated from impedance spectra by using an equivalent circuit with multiple Warburg elements. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.2138672] All rights reserved.