The electrochemical characteristics of thermally prepared oxide films of nominal composition Ir0.3Ti(0.7-x)SnxO2 were examined as a function of x by ac impedance measurements. For potential values in the double layer region, the impedance behavior observed at low frequency was attributed to the double layer capacitance of the oxide/electrolyte interface, while at high frequency it was attributed to a mass transport limited process occurring in difficult-to-access oxide regions. The main source of ohmic resistance of the system is the solution resistance and low proton transport, necessary for the Ir(III)/Ir(IV) redox transitions to occur in more difficult to reach oxide regions. The electrocatalytic properties as a function of composition, studied using the OER in 1.0 mol dm(-3) HClO4 as a model reaction, revealed ternary mixture have slightly superior real catalytic properties when compared to the binary mixtures. The behavior of the charging processes as a function of composition was analyzed based on the double layer parameters.