3,5-Dithiophene-2-yldithieno[3,2-b;2',3'-d]thiophene (Thy(2)DTT) and ethylenedioxythiophene (EDOT) were electro-copolymerized on glassy carbon electrode (GCE) in 0.1 M sodium perchlorate (NaClO4)/acetonitrile (ACN)/dichloromethane (CH2Cl2) (8:2) solution. Poly(Thy(2)DTT-co-EDOT)/GCE thin film was characterized by various techniques, such as Cyclic Voltammetry (CV), Fourier Transform Infrared Spectroscopy - Attenuated Transmittance Reflectance (FTIR-ATR), Scanning Electron Microscopy - Energy Dispersive X-ray analysis (SEM-EDX) and Electrochemical Impedance Spectroscopy (EIS). The effects of monomer mole fractions (mole fraction, X-Thy2DTT = n(Thy2DTT/nEDOT) + n(Thy2DTT)) (0.5, 0.66 and 0.83) during the preparation of modified electrodes were examined by EIS. Capacitive behaviors of the modified GCE were defined via Nyquist, Bode-magnitude, Bode-phase and Capacitance plots. The circuit model was used to fit the theoretical and experimental data through Kramers-Kronig Transform test. The lowest frequency capacitance (C-LF) value was obtained as C-LF = 0.89 mFcm(-2) for poly(Thy(2)DTT). However, the highest C-LF was obtained for the copolymer as C-LF = 1.11 mFcm(-2) for X-Thy2DTT = 0.66 and 0.83. Potential application of the copolymer could be energy-storage devices.