The oxygen evolution reaction (OER) on IrO2-Ta2O5 mixed oxide electrodes in H2SO4 solution was studied by performing quasi-stationary current-potential and electrochemical impedance spectroscopy (EIS) measurements. The uncompensated resistance corrected Tafel lines displayed two distinct linear regions, with one of the slope close to 60 mV dec(-1) in the low potential region and the other close to 130 mV dec(-1) in the high potential region. The kinetics equations based on the proposed OER mechanism were derived and were used to simulate the current-potential curve. A mathematical deduction of EIS data was also carried out based on one state-variable theory. Both the polarization curve and impedance spectra were well approximated by kinetics analysis. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.