The electrochemical oxidation of ethyl alcohol has been studied at platinum electrodes in aqueous carbonate solutions employing cyclic voltammetry (CV), chronoamperometry, chronocoulometry, and impedance measurements. Two anodic CV peaks are observed during the positive scan and only one cathodic peak is observed during the negative scan when the alcohol concentration is low. At higher alcohol concentrations, only one anodic CV peak is observed during the anodic scan due to the electrode passivation beyond the first anodic peak potential, and an anodic peak attributable to the depassivation of the electrode is observed during the reverse scan. The results are consistent with the formation of passive films of the electrode surface by a reaction of platinum or its oxide with ethoxy free radicals. The formation of passive films has been confirmed by the temperature dependency of voltammograms and impedance measurements.