Ordered mesoporous carbons (COU-1 and COU-2) were synthesized using a soft-templating method. Then, COU-1 and COU-2 were activated using KOH to improve their porosity. Galvanic charge-discharge cycles were employed to investigate the electric double-layer capacitance of the ordered mesoporous carbons in an aqueous electrolyte. The contributions of the surface areas of the ultramicropores (d < 0.7 nm) and micro-and mesopores (d > 0.7 nm) to the capacitance were evaluated using a simple model. The ultramicropore surface area hardly contributed to the capacitance. On the other hand, the surface area of the larger pores (d > 0.7 nm) strongly contributed to the capacitance, suggesting that pores larger than 0.7 nm are necessary for the fast diffusion of sulfate ions to the pore surface. The capacitance of the ordered mesoporous carbons was higher than that of disordered mesoporous carbon, probably because of the micropores in the uniform thin pore walls and regularly interconnected uniform mesopores in the former case.