Raman spectra of both supported and unsupported Fe/Mo/O catalysts of the type used for the partial oxidation of methanol to formaldehyde were obtained while this reaction was proceeding over the catalyst surface. No changes in band locations or relative peak intensities associated with these mixed metal oxides were detected in the presence of reactant and product species. Moreover, no spectral features which could be attributed to adsorbed species could be detected under reaction conditions. Band intensities in the Raman spectra were related to the extent to which the catalysts were reduced; fully oxidized catalysts were stronger Raman scatterers than partially reduced catalysts. Although differences in color were noted between fresh and used catalysts, the Raman and Mössbauer spectra of these catalysts were identical. Calcination of used catalysts in an oxygen environment at 500 °C was sufficient to restore partially reduced catalysts to their original fully oxidized states.