The Fe3+ reduction reaction was studied at Pt and polyaniline rotating disk electrodes by steady‐state and impedance methods with the aim of testing the possibility of achieving the charge transfer resistance of a redox reaction mediated by a conducting polymer film by ac impedance. was obtained as a function of electrode potential and rotation rate by nonlinear least squares fitting of a previously developed kinetic equation to the experimental data. These values were combined with steady‐state ones to calculate and .