Activated carbon supports a high power density, but has limited specific capacity. To increase the capacity of activated carbon, ruthenium oxide was loaded into various types of activated carbon by suspending the activated carbon in an aqueous RuCl3 solution followed by neutralization. Although the Brunauer-Emmett-Teller surface area of the activated carbon decreased upon ruthenium oxide loading compared to that of the starting material, its capacitance increased. The maximum capacity obtained in this study was 308 F/g for activated carbon loaded with 7.1 wt % ruthenium, an increase of about 20%.