Copper-silica composites prepared by the sol-gel method were thermally treated at 110, 500, 900 and 1100 degreesC and studied by nitrogen adsorption, powder X-ray diffraction and temperature programmed reduction. Samples treated at 500 degreesC showed the highest surface area and copper exposed on the surface of the silica matrix resulting in a high catalytic activity for carbon monoxide oxidation. Treatment at 900 and 1100 degreesC produced the crystallization/densification of the samples with a strong decrease in sample area. As a result of these processes, the copper species were entrapped inside the vitreous silica matrix and the catalytic activity for carbon monoxide oxidation was strongly reduced.