The electrochemical oxidation of homogentisic acid (HGA) as an important biological molecule has been studied in aqueous and mixed acetonitrile-water solutions using cyclic voltammetry. The effects of pH, HGA concentration, time window of the chosen electrochemical method and different solvents were studied to investigate the proton and electron transfer processes. The oxidation product of HGA in aqueous solution is stable in acidic, neutral and weakly alkaline media at the time scale of cyclic voltammetry. The electrooxidation process of HGA in aqueous solution follows E-q mechanism. In mixed acetonitrile-water solution, the electrooxidation process of HGA follows an EqCiEq mechanism. The experimental results indicate that the subsequent chemical reaction of dimerization is more probable for the oxidized form of HGA. It is shown that the separation of the cathodic and anodic peak potentials, Delta E-p, in the mixture of acetonitrile-water is greater than that in aqueous solution and it increases with the increase of acetonitrile content in the mixture. (C) 2014 Elsevier B.V. All rights reserved.