Impedance measurements of the oxygen evolution reaction on a composite electrode prepared from an ethylene-propylene terpolymer (EPDM) admired with acetylene carbon black have been carried out. A theoretical analysis of measured impedance is presented. The mechanism of the oxygen evolution reaction has been determined. The oxygen evolution reaction is composed of two electrochemical steps and one chemical step. The slowest step for the oxygen evolution reaction is the first charge transfer step which is based on the formation of an intermediate OHAd adsorbed species.