The electrochemical reduction of oxygen on glassy carbon (GC) electrodes grafted with anthraquinone (AQ) has been studied using the rotating ring-disk electrode technique. Grafting was achieved by the electrochemical reduction of the corresponding diazonium salt and the effect of AQ surface concentration on the kinetics of oxygen reduction has been investigated. The two-electron reduction of oxygen to hydrogen peroxide was observed for all the quinone-modified electrodes studied and the catalytic activity of the electrodes for O-2 reduction was dependent on the AQ surface concentration. The kinetic parameters of oxygen reduction on GC/AQ electrodes in 0.1 M KOH were determined as a function-of AQ surface concentration considering a surface redox catalytic cycle model for quinone-modified electrodes. The rate constant of the chemical reaction between the semiquinone radical anion of AQ and molecular oxygen has been determined.