Al2O3-MgO mixed oxides of different Al/Mg mol ratios were prepared and characterized with X-ray diffraction, N-2 adsorption and temperature-programmed desorption of ammonia and carbon dioxide. An increase of Al/Mg mol ratio enhances the catalyst acidity with concomitant decrease of the basicity. In the reaction of 2-propanol, the propene selectivity increases with the catalyst acid amount, whereas the selectivity ratio of 2-propanone to propene is parallel to the catalyst base amount. Accordingly, the conversion of 2-propanol can be utilized as a test reaction for characterizing the acid-base property of the mixed oxides.