he effect of pore size on the response characteristic of an electric double layer capacitor (EDLC) was closely examined. A series of phenol-resin-based activated carbon (AC) samples was prepared as average pore size from 0.94 to 1.68 nm by KOH activation by varying the activation temperature and KOH/carbonized phenol-resin ratio. The impedance properties of pouch-type EDLC cells prepared using AC samples were evaluated by applying an alternating current at 3 V between 10 mHz and 100 kHz for confirming the response characteristic. The cell based on the AC with a largest pore size (1.68 nm) showed fast response frequency, and had a high dielectric relaxation time constant as calculated from the response frequency value. The AC with the largest pore size, which consisted of both micropores (>1 nm) and mesopores (2-4 nm), was confirmed to facilitate extremely low electrolyte-diffusion resistance during the formation of the electric double layer, implying that the large pores lead to fast and stable response frequency. The presented findings suggest that AC with a largest pore size as the electrode leads to superior capacitance and response frequency characteristics in the alternating current than those of an AC with a smaller pore size.