The oxygen evolution reaction (OER) in alkaline solution has been studied for various Ti supported Ir0.3Ti(0.7-x)PtxO2 anodes with 0 less than or equal to x less than or equal to 0.7 by impedance measurements (EIS) at potentials between -0.6 and 1.0 V vs. Hg/HgO (NMOE). The electrical parameters of the electrode solution interface were obtained by fitting the experimental impedance data either to a R(Ohm)(R(f)C(f))(R(ct)C(dl))L (for the Ir0.3Ti0.7O2 electrode) or a R’(Ohm)(QR(ct))L (for PtOx-containing electrodes) equivalent circuit, where Q = constant phase element. The impedance spectrum in the inert region, -0.6 to 0.45 V, is an almost vertical line, indicating that the interfacial impedance is essentially capacitive. The ohmic component obtained from EIS (R(Ohm) = 2.2 Ohm cm(2)) for the Ir0.3Ti0.7O2 electrode is consistent with the value obtained from the Tafel plot (R(Ohm) = 2.4 Ohm cm(2)). The substitution of Pt for Ti in the binary system results in a dramatic increase in the R(ct) value, ie, the reaction becomes more difficult in the presence of this oxide. It was also observed that the introduction of PtOx causes large morphological changes in the binary system. The different behaviour of the IrO2 + TiO2 system from the other oxide compositions is attributed to the instability of the latter oxides in alkaline solution.