On the example of Fenton reaction we present the applicability of the impedance spectroscopy for complete characterization of the catalytic processes, in which the electrochemical step (E) is followed by a homogeneous chemical reaction regenerating the depolarizer (C'). Provided a simplified model together with the potential dependence of all impedance parameters allow for a rapid and precise determination of all kinetic and thermodynamic parameters of the EC' type processes. For the Fenton reaction, the formal potential, number of exchanged electrons, heterogeneous rate constant, homogeneous reaction rate constant, cathodic and anodic electron transfer coefficients, and both diffusion coefficients of the redox mediator were precisely determined by using EIS solely. The majority of these parameters have been determined here for the first time while the others are in good agreement with previous literature reports. Although, we discuss particular cases of Fenton reaction, the analysis provided in this report has more general meaning and can be applied to other electrocatalytic processes, in which a redox mediator is used as an electron carrier. (C) 2015 Elsevier Ltd. All rights reserved.