In this study, the capacitances of electric double layer capacitors (EDLCs) with nanocomposite electrodes were examined by analyzing their charge–discharge characteristics and cyclic voltammograms. In addition, the internal resistance of these EDLCs was evaluated using two kinds of conductive nanofillers: acetylene black (AB) and Ketjenblack (KB). Usually, KB exhibits higher electronic conductivity than AB. The temperature dependence of the capacitance and internal resistance of the prepared EDLCs at 0–50°C using an aqueous electrolyte, organic electrolyte, and two kinds of ionic liquids was evaluated. Moreover, the influence on the capacitance and internal resistance when KB containing a surface functional group is used as the conductive nanofiller of the polarized electrode was examined. It was found that the KB-containing EDLCs showed fairly high capacitance (150–210F/g) compared to EDLCs containing AB with the aqueous electrolyte. In addition, a maximum specific capacitance of 252F/g was obtained in EDLCs containing 20wt.% KB with a large amount of the surface functional group. Reduction–oxidation reactions were thought to occur at the interface between the electrolyte and surface functional group, which increased the specific capacitance of the EDLCs.