To study the decomposition of methyl alcohol (CH3OH) by a photocatalytic reaction, TiO2/WO3 bilayers composed of TiO2 and WO3 films were deposited using reactive sputtering at the working gas pressure P-W of 1 and 3 - 8 mTorr, respectively. The optical transmittance spectra of as-deposited TiO2/WO3 bilayers monotonically decreased with decreasing wavelength in the range of 200-900 nm. When depositing WO3 films, the adsorption edge shifted to a higher wavelength of about 400 nm with decreasing P-W. These spectra may depend on the properties of WO3 films, rather than those of TiO2 films. As expected, the bilayer can adsorb much more visible light compared to TiO2 single layers. From the measurement of Fourier transform infrared transmittance spectra, CH3OH can be decomposed strongly into CO2 and H2O molecules, compared to the TiO2 single layer. When the TiO2/WO3 bilayer was irradiated with artificial sunrays for 130 min, the formation rate of CO2 molecules was about two times as fast as that in the Ti02 single layer. We found that the decomposition of CH3OH may depend on the crystallinity and optical properties of WO3 underlayers. (C) 2003 American Vacuum Society.