RuO2-SnO2 coatings supported on titanium were characterized in morphology using a high resolution scanning electron microscope and an atomic force microscope and in composition using a scanning Auger microscope. Ruthenium was segregated in island-like deposits in the case of RuO2-rich electrodes and along cracks for SnO2-rich electrodes where tin was localized in the macroscopically flat plane consisting of ultrafine particles. The ultrafine particles found on SnO2-rich electrodes, which were smaller than those found for RuO2-rich electrodes, contributed to the large active surface area of the electrode.