The kinetics and mechanism of the full reduction of a thin RuO2 film with a stoichiometric (110) surface on Ru(0001) by H2 has been studied in the temperature range of 100 to 400 C at 10-2 to 10 -4 Pa. The reduction kinetics is dominated by the creation of oxygen vacancies and their annihilation upon transformation of RuO2 into metallic Ru. The temperature-dependent reduction rate increases linearly with H2 pressure. In the temperature range of 100 up to 200 C, initially hydrogenation of the RuO2(110) surface occurs. Next, oxygen vacancies are created due to desorption of water vapor, which accelerates the reduction by place exchange of oxygen bulk atoms with an activation energy of 0.45 eV. In the temperature range of 200 to 300 C, slow reduction of RuO2 by H2 already occurs in the initial period with an activation energy of 0.48 eV and is followed by faster reduction. In the temperature range of 300 to 400 C, the reduction of RuO2 starts immediately when exposed to H2 and the activation energy (0.48 eV) is similar to the activation energy in the lower temperature range (100 to 200 C). Apparently, the annihilation of oxygen vacancies during reduction is more prominent with increasing temperature. © 2012 American Chemical Society.