Sol-gel magnesia-silica mixed oxides were prepared with tetraethoxysilane (TEOS) and magnesium ethoxide as molecular precursors. While still at the fluid phase before gelation, a solution of copper acetylacetonate was added. After gelation, the solids thus obtained were sulfated in two ways: by conventional impregnation and by an in situ impregnation with H2SO4. The solids were characterized by TPD (NH3 and CO2). The solids impregnated in situ, containing 4.0 and 6.7 mol% of MgO show a high acidity. The mixed oxides showed high specific surface area values when the gelation is carried out at pH 3; however, at pH 9, areas three times smaller were obtained. Their catalytic activity was studied using the decomposition of 2-propanol as a test reaction.