Composite electrodes for surpercapacitors were fabricated by depositing polyaniline (PAn) on the surface of activated carbon powders (ACP) by using the electrochemical method. Their capacitance values were measured in the 1M H2SO4 aqueous electrolytes containing SiO2, which showed the conductivity values of 2.6 × 10−1, 2.3 × 10−1, and 1.5 × 10−1 S/cm for their liquid, gel, and solid-like gel states, respectively, according to the content of SiO2. The Pt/ACP/PAn electrodes showed a specific capacitance value of 270F/g in the 1M H2SO4 solid-like electrolyte, which value was larger than the capacitances of 144 and 209F/g for the Pt/ACP and the Pt/PAn, respectively. This result suggests that the capacitance performance of the ACP can be improved by compositing with PAn, and the 1M H2SO4 solid-like electrolyte is suitable for the use in the supercapacitor.