Electrochemical synthesis of a new copolymer film based on azulene and 3-thiophene acetic acid was accomplished by using tetrabutylammonium hexafluorophosphate and acetonitrile as electrolyte. Both homopolymers and the copolymer were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and in situ UV-Vis spectroscopy. The effect of monomer concentration on electropolymerization process was studied by the cyclic voltammetry technique. Electrochemical impedance spectroscopy is used to study the characteristics of the film structures and kinetics, as well as the mechanisms for charge transfer and ion transport at polymer film/electrolyte interface. Fourier transform infrared spectroscopy results confirm the presence of both monomers in the resulting copolymer. Spectroelectrochemical measurements show the changes in the colour of the polymeric films with applied potentials. The synthesized copolytner film was used in voltammetric sensor development for H2O2 determination. A low detection limit of 10 nM H2O2 has been obtained.