The surface interaction between differently prepared tin oxide samples and CO was studied by Diffuse Reflectance Infrared Fourier Transform (DRIFT)-spectroscopy at room temperature. As samples, commercial powders (Merck) and home-made powders obtained by a sol-gel preparation were used. Several bands corresponding to isolated and rooted OH groups, coordinated water and condensed water in two forms: ordered lavers of water molecules and water in the liquid form, were found. Their appearance and intensity depended on the sample origin and storing conditions. Moreover, the spectra of all samples show bands corresponding to different hydrated protons (H3O+, H5O2+) and carbonate ions of different intensities. To get information about the interaction between SnO2 powders and CO, in-situ measurements were conducted. We found that differently bound water and specific surface OH-groups react with CO and that surface carbonate ions dissociate because of acidic intermediate products. As a result, different bands corresponding to physisorbed CO appear at approximately 2200 cm(-1), together with changes in the region corresponding to covalent bound chelating and bridging bidentate carbonates and carboxylate (between 1700 and 1000 cm(-1)).