FTIR spectroscopy coupled with mass spectrometry has been used to study the mechanism of methanol oxidation at low temperatures on nanostructured Au/CeO2 and Au/TiO2 catalysts. Activity and selectivity toward CO2 have been investigated through simultaneous analysis of adsorbed surface species and gaseous species, and some key steps in the oxidation pathway, active sites, and intermediate species are proposed. Among the detected species, some kinds of methoxy species formed on the support were identified as intermediates, which further transform into formates whose oxidation was found to be the rate-determining step for the reaction. The role of the support and the noble metal in the mechanism are revealed using operando spectroscopy.