The electrochemical impedance spectroscopy of oxidized poly(3,4-ethylenedioxythiophene) (PEDOT) electrodeposited on a platinum electrode surface was studied in LiClO4+propylene carbonate solutions. The effects of the electrolyte concentration, the applied potential, and the film thickness were studied. The impedance responses were analyzed within a dual transmission line model. Results showed that the ionic conductivity of the p-doped PEDOT film was controlled by the electrolyte solution in pores, and the interfacial impedance resulted from the double-layer capacitance. A linear variation of the redox pseudo-capacitance and the ionic film resistance as a function of the film thickness was observed. These results showed the porous nature of the PEDOT film deposited on the electrode surface. (C) 2003 Elsevier B.V. All rights reserved.