The effects of ionic strength and film thickness on the transport properties of poly(o-aminophenol) (POAP) film electrodes were studied by impedance spectroscopy. The dependences of the characteristic impedance quantities (Warburg coefficient, resistance and redox capacitance at low frequency) on these external variables were interpreted on the basis of two models : a transmission line and a modified electron hopping model. Analysis of experimental data by means of the transmission line model allowed us to separate the charge transport process within the film in terms of electronic and ionic contributions represented by the diffusion constants, D-e and D-x, respectively. Application of the electron hopping model only gave an effective diffusion coefficient, D-eff. The diffusion coefficients D-e and D-x, in the first case, and D-eff in the second case, depend upon the ionic strength and film thickness. Moreover, D-eff is very close to D-e. This proves that charge propagation is dominated by electron transport in this polymer.