The relationship between the properties of ruthenium oxide and its electrode performance with respect to methanol electro-oxidation was investigated using a Pt–RuO2 nanocomposite thin-film electrode fabricated by a cosputtering system. The performance of the nanocomposite electrode, consisting of a Pt nanophase and a RuO2, was modified by heat treatment at different temperatures (100, 250, and 400 °C) which altered the proton and electron contributions in the electrodes. The transport of protons produced during methanol electro-oxidation in the Pt–RuO2 nanocomposite electrode was directly observed during electrochemical reaction by means of the ectrochromism of RuO2. It is concluded that improved electrical conduction that maintains the transport of protons is responsible for the enhanced electro-oxidation of methanol for 250 °C Pt–RuO2. © 2003 American Institute of Physics.