Oxygen reduction was investigated at iron(III) octaethylporphyrin chloride adsorbed on a glassy carbon electrode. The title porphyrin was adsorbed irreversibly and strongly on the surface of a glassy carbon electrode. The electrochemical behavior and stability of the modified electrode were investigated using cyclic voltammetry, chronoamperometry and rotating disk electrode methods. The modified electrode showed clear but modest electrocatalytic activity for the reduction of oxygen to a mixture of water and hydrogen peroxide in buffered solutions on both the acid and basic sides of neutral with the domination of an overpotential of about 690 mV and an increase in peak current. The heterogeneous rate constant for the reduction of O-2 at the surface of the modified electrode and the diffusion coefficient of oxygen were determined by rotation disk electrode voltammetry using the Koutecky-Levich plots. In addition, iron(III) octaethylporphyrin chloride exhibited strong catalytic activity toward the reduction of H2O2. (C) 2003 Elsevier B.V. All rights reserved.