The impedance response of electrochemically synthesized Poly-(o-toluidine) (POT) films was measured, in the potential region corresponding to polymer oxidation (0.25 V < E < 0.65 V vs the Reversible Hydrogen Electrode; RHE), in HClO4 solutions as a function of the film thickness and the electrolyte concentration. The thickness is expressed in terms of the voltammetric charge, Q, required to redox switch the firm in the pure supporting electrolyte. In the conducting state (E similar to 0.6 V vs RHE) the characteristic impedance parameters (low frequency resistance, R-LF, capacitance, C-LF, and the Warburg coefficient, sigma) are independent of the electrolyte concentration but depend markedly on Q. C-LF increases linearly with the thickness. For thick films (Q > 30 mC cm(-2)) both R-LF and sigma remain approximately constant. In the region of small thickness, R-LF and sigma increase as the charge decreases. This is interpreted in terms of the polymer morphology. For thin films, this type of polymer has a compact structure through which ion motion into the polymer is slow. Otherwise, thick films develop fibrilar aggregates on top of the compact layer which can explain the constancy of R-LF and sigma. The analysis of the potential dependence of equivalent circuit elements through impedance models allows one to conclude that ionic motion is the rate controlling step for charge transport in this polymer.