In this study, mixed active material electrodes, composed of an activated carbon (MSP20) and LiCoO2, were prepared as cathodes for a high-capacitive hybrid capacitor. The electrochemical properties of (MSP20+LiCoO2)/Li cells were examined in terms of the weight composition and the particle size of LiCoO2 powder in the electrodes. As adding more LiCoO2 powders in the electrode, the volumetric capacity (mAh/ml) of the electrode became higher. In order to examine the size effect on the electrochemical performance, the LiCoO2 powders were modified by ball milling. The (MSP20+LiCoO2)/Li cells using 10 and 20 wt.% of 30h-milled LiCoO2 powder exhibited the lower internal resistivities and the better capacity retentions after 100 charge-discharge cycles than those using 10 or 20 wt.% of raw LiCoO2 powders.