A new electric double layer capacitor (EDLC) was constructed by using polymer hydrogel electrolyte prepared from cross-linked potassium poly(acrylate) and a KOH aqueous solution. The electrochemical characteristics of the EDLC cell were investigated by cyclic voltammetry and charge/discharge cycle testing compared with those of the cell using only a KOH aqueous solution as an electrolyte. As a result, it was found that the cell with the polymer hydrogel electrolyte exhibited higher capacitance and better cycle performance than that with the KOH aqueous solution. It was suggested by impedance spectroscopy that the higher capacitance could be ascribed to pseudocapacitance. These results indicate that the polymer hydrogel electrolyte has potential applicability to the EDLCs as an electrolyte with good performance. (C) 2002 The Electrochemical Society.