Deactivation of a RuO2-IrO2-TiO2/Ti oxide anode was investigated during an accelerated life test in 0.5 mol dm(-3) NaCl by use of cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy/energy-dispersive X-ray analysis. The variations in double-layer capacitance, film resistance, and charge-transfer resistance during electrolysis were recorded at different potentials. A comprehensive deactivation mechanism of titanium anodes has been proposed by the growth of an insulating TiO2 layer at the coating-substrate interface due to the titanium substrate oxidation. The impedance interpretation of the deactivation mechanism in chloride solutions changes with an increase in potential due to an increase in oxygen evolution on the anode surface at higher potentials.