Diffusion processes during the oxidation of alloys involving noble metals are analyzed theoretically. An oxide film of uniform thickness is stable only if diffusion in the alloy is relatively rapid compared with diffusion in the oxide of the less noble metal. Otherwise, there is the tendency to form a rugged alloy‐oxide interface. The oxidation rate is calculated for the limiting case of a scale consisting of protruding sections of the oxide of the less noble metal interspersed with slender trunks of alloy rich in the more noble metal. Under these conditions, the oxidation rate of alloys containing up to 50% of noble metal is supposed to be of the same order of magnitude as the oxidation rate of the less noble metal in its pure state.