Ion penetration into pores during double-layer charging/discharging has been investigated by analyses of potentiostatic current transients (PCTs) and cyclic voltammograms (CVs) experimentally measured on porous carbon electrodes with pore fractality. From the analyses of the cathodic PCTs measured on microporous electrodes, it was found that the PCTs showed ideal behavior with a slope of -0.5 in the earlier stage, indicating that the change in the resistance-capacitance (RC) time constant distribution produced by pore fractal dimension in the micropore size range is too small to affect the shape and value of the PCT. The cathodic PCTs measured on meso/macroporous electrodes exhibited anomalous behavior with a slope lower than -0.5 in the earlier stage due to the considerably wider RC time constant distribution. From the analyses of the cathodic PCTs measured on multifractal electrodes, it is strongly suggested that the current decays more rapidly with increasing relative volume fraction of larger-sized pores. From the analyses of the measured CVs, it is experimentally confirmed that the higher relative volume fraction of larger-sized pores enhances the rate capability gamma, which yields us the higher power density, but it reduces the double-layer capacitance, which provides us the lower energy density. (c) 2007 The Electrochemical Society.