Hydrous ruthenium oxide was formed by a new process. The precursor was obtained by mixing the aqueous solutions of RuCl3·xH2O and NaHCO3. The addition of NaHCO3 led to the formation of an oxide with extremely fine RuO2 particles forming a porous network structure in the oxide electrode. Polyethylene glycol was added as a controller to partly inhibit the sol-gel reaction. The rate capacitance of 530 F·g-1 was measured for the powder formed at an optimal annealing temperature of 210°C. Several details concerning this new material, including crystal structure, particle size as a function of temperature, and electrochemical properties, were also reported. In addition, the rate capacitance of the composite electrode reached 800 F·g-1 after carbon black was added. By using the modified electrode of a RuO2/carbon black composite electrode, the electrochemical capacitor exhibits high energy density and stable power characteristics. The values of specific energy and maximum specific power of 24 Wh·kg-1 and 4 kW·kg-1, respec-tively, are demonstrated for a cell voltage between 0 and 1 V. Hydrous ruthenium oxide was formed by a new process. The precursor was obtained by mixing the aqueous solutions of RuCl3.xH2O and NaHCO3. The addition of NaHCO3 led to the formation of an oxide with extremely fine RuO2 particles forming a porous network structure in the oxide The weight capacitance of 530 F · g-1 was measured for the powder formed at an optimal annealing temperature of 210 ° C. Several Details from this new material , including crystal structure, particle size as a function of temperature, and electrochemical properties, were also reported. In addition, the rate capacitance of the composite electrode reached 800 F · g-1 after carbon black was added. a RuO2 / carbon black composite electrode, the electrochemical capacitor exhibits high energy density and stable power characteristics. The values ​​of specific energy and maximum specific power o f 24 Wh · kg -1 and 4 kW · kg -1, respec- tively, are demonstrated for a cell voltage between 0 and 1 V.