Platinum/SiO2 sonogel has been compared with the corresponding xerogel and an impregnated catalyst. The thermal behavior, the FTIR spectra and the pyridine adsorption show that Lewis acidity is present in the impregnated sample. In the sonogel, Lewis acidity turns to be very low and insensitive to desorption temperature. In the xerogel, both Lewis and Bronsted acidity was observed. In each sample, reduction in situ (without hydrogen flow) of the metal phase is determined by the OH content. Platinum is highly reduced in the sonogel, partially reduced in the xerogel and very slightly reduced in the impregnated sample.