Fullerene-activated carbon composite electrodes were prepared and their charge/discharge characteristics were studied for use in a high power electric double-layer capacitor. The capacitance of the C60-loaded activated carbon fiber (ACF) electrodes became greater than that of the unloaded ACF at charge/discharge current densities above 50mA/cm2. In order to obtain a highly dispersed C60-loaded electrode, an ultrasonic treatment was performed. The size of the C60 agglomerate decreased from 1–2 to 0.1μm or less, and the capacitance of the C60-loaded ACF electrodes increased with an increase in the ultrasonic treatment time. A higher capacitance of 172F/g was obtained at 50mA/cm2 on a 1wt% C60-loaded electrode with ultrasonic treatment, and the C60-loaded ACF electrode also showed a higher cycle performance.