Titania-zirconia mixed oxides with various ZrO2 content in TiO2 (10, 50 and 90 wt.%) were prepared by the sol-gel method. High specific surface areas (77-244m(2)/g) were obtained. Acidity determined by NH3-TPD and FTIR-pyridine adsorption showed that in mixed oxides the number of acid sites is dramatically increased; it varies from 173 mumol NH3/g for TiO2 to 1226-1456 mumol NH3/g for the mixed oxides. FTIR-pyridine adsorption showed the presence of Lewis sites in the catalysts. Basic sites were identified by FTIR-CO2 adsorption, suggesting the formation of mixed oxides with acid-basic properties. XRD spectra identified anatase in the TiO2 rich region, amorphous material in the mixed oxide 50-50 TiO2-ZrO2 and tetragonal and monoclinic crystalline phases in the ZrO2 rich region. Activity in the isopropanol decomposition showed a good correlation between the acid-basic properties and the selectivity to propene, acetone and isopropyl ether. The latter was found as a product which mainly depends of the acid sites density. (C) 2004 Elsevier B.V. All rights reserved.