Zirconia/silica mixed oxides were prepared by the sol-gel method at pH 3 and 9 using tetraethoxysilane and zirconium acetate at 1.3, 4.0, and 6.7 wt % ZrO2. In acidic preparations, high specific BET areas were obtained. 2-Propanol decomposition was used as the reaction test. It was found that the selectivity to propene or acetone is a function of the preparation medium. In acidic preparations, acid sites were developed and high selectivity to propene was observed; formation of Zr-O-Si bonds in bulk and surface was suggested. By the contrary in basic preparations, the main product was acetone. In such a case the formation of Zr-O-Si bonds and pure ZrO2 deposited on the silica surface is proposed.