Activated carbon (AC) fiber cloths and hydrophobic microporous polypropylene (PP) membrane, both modified by plasma-induced graft polymerization of acrylic acid (AAc) under UV irradiation, and filled with saturated lithium hydroxide solution were used as electrodes, a separator and electrolyte in electric double layer capacitors (EDLCs). The modification process changed the hydrophobic character of AC and PP materials to hydrophilic, made them wettable and serviceable as components of an electrochemical capacitor. The presence of poly(acrylic acid) on the AC and PP surface was confirmed by SEM and XPS methods. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry and galvanostatic charge–discharge cycle tests and also by impedance spectroscopy. At the 1000th cycle of potential cycling (1Ag−1) the specific capacitance of 110Fg−1 was obtained with a specific energy of 11Whkg−1 at power density of 1kWkg−1. The above results provide valuable information which may be used when developing novel compositions of EDLCs.