Electrochemical reduction of dioxygen on an iron(III)-tetra-o-ureaphenylporphyrinosilica matrix surface ((o)-FeTUPPS) obtained by attachment of the iron porphyrin tetraurea to a silica matrix through the sol-gel process was studied. Cyclic voltammetry and chronoamperometry techniques using as working electrode a carbon paste electrode modified with (o)-FeTUPPS, showed that (o)-FeTUPPS catalyzed O-2 reduction at -0.34 V vs SCE in 0.5, mol.L-1 KCl solution at pH 6. The electrode showed a linear and reproducible response to O-2 concentrations in the range ca. 0.5 and 11 mg.L-1 and was chemically stable under various oxidation-reduction cycles. From rotating disk experiments it was concluded that dissolved O-2 was reduced at the electrode surface to H2O2 in a two-electron process. Copyright (C) 2002 Society of Porphyrins & Phthalocyanines.641858527532