The electrochemical synthesis of polythiophene (PTh) has been investigated on copper electrode, in LiClO4 containing acetonitrile medium (ACN-LiClO4). It was shown that a corrosion protective PTh film cannot be obtained on copper surface, by direct electro oxidation of thiophene, because the surface could not be passivated sufficiently and copper dissolution continued in the monomer oxidation potential region. This prevented the deposition of homogeneous polymer film on the surface. The synthesis of polythiophene (PTh) was achieved on copper electrode, which had been previously coated with very thin polypyrrole (PPy) film. The PPy film was obtained in 0.1 M monomer containing aqueous oxalic acid solution. Then, the synthesis of PTh film was achieved on this PPy-coated copper electrode, in 0.1 M thiophene containing ACN-LiClO4. The corrosion behaviour of PPy/PTh-coated copper was investigated in 3.5% NaCl solution. For this aim, electrochemical impedance spectroscopy (EIS), anodic polarization curves and open circuit potential-time (E-vcp-t) diagrams were utilized. It was shown that the PPy/PTh coating could provide important protection against copper corrosion for considerable immersion periods. (c) 2005 Elsevier B.V. All rights reserved.