Poly(3,4-ethylenedioxythiophene) polymer film (PEDOT-IL) was electrosynthesized in the ionic liquid (IL) 1-ethyl-3-methylimidazolium hydrogen sulphate (EMIMHSO4) medium, which also contains 0.1 M LiClO4 in ACN. For comparison reasons in terms of structure and electrode capacitance performance, PEDOT film was also synthesized electrochemically without IL. The SEM results show that PEDOT-IL film has more porous surface and fine textures with nanometer-diameter than PEDOT polymer. Different electrochemical methods including galvanostatic charge-discharge (CD) experiments, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were carried out to investigate the applicability of the system as a redox supercapacitor for both polymers. PEDOT-IL electrode shows higher optimum specific capacitance than PEDOT film. Additionally, the symmetrical supercapacitor was assembled from two PEDOT-IL electrodes in LiClO4/ACN medium and exhibited a maximum specific capacitance of 107 F g(-1), an energy density of 11.5 Wh kg(-1) at a power density 13 kW kg(-1), and an excellent cycle life of 96% specific capacitance retention after 1000 cycles.