Thermally prepared oxide films (2 mu m) of nominal composition Ir0.3Ti0.7O2 were prepared at 350, 400, 450 and 500 degrees C On a Ti support. Electrochemical impedance spectroscopy (EIS) at constant potential was used in the range 0.4 to 1.6 V (rhe). The results were fitted by the equivalent circuit R(Omega)(R(f)C(f))(R(ct)C(dl))L. The R(Omega) values obtained by EIS agree with the data derived from kinetic studies. The high R(ct) value of the 350 degrees C oxide layer is attributed to the incomplete decomposition of the precursor so that some of the underlying insulating TiO2 layer remains uncovered. This view is corroborated by SEM and CV studies. Oxide layers prepared at higher temperatures are stable, the R(ct) values increasing with calcination temperature. This is attributed to crystallite size increasing with temperature, resulting in a lower number of active sites being exposed. For all electrodes, R(ct) decreases with increasing potential. C-dl depends on both surface area and applied potential. At T > 350 degrees C, C-dl diminishes as temperature increases, which is due to decrease in the active surface area. Analogously, C-dl is observed to increase with increasing potential, which is associated with the heterogeneity of the electrode surface.