A SnO2-supported WO3 catalyst has been prepared by wet impregnation. X-ray photoelectron spectroscopy, diffuse reflectance IR Fourier transform spectroscopy, and X-ray diffraction data suggest the presence of small clusters of W coordinated to oxygen atoms on the tin oxide surface. The chemisorption of methanol and formaldehyde on the catalyst has been studied at atmospheric pressure and under high vacuum (HV) conditions. Methanol chemisorbs both molecularly and dissociatively on the supported oxide surface. Formaldehyde produced by the dissociative chemisorption of CH3OH has been observed both under HV and at atmospheric pressure conditions. The temperature increase causes the formation of COP and of formaldehyde polymers. The presence of oxygen in the reaction mixture facilitates the decomposition to CO2 and the formation of formaldehyde.