Ozone adsorption has been studied by IR spectroscopy at low temperature. Although alumina is more acidic than TiO2, as shown by pyridine adsorption, IR spectroscopy did not detect O-3 species adsorbed on strong Lewis Al3+ sites. However, O-3 decomposition occurred and pyridine specific poisoning evidenced that such sites were involved in the decomposition. Quantum chemistry calculations confirmed such a result and specified that the remaining O(D-1) resulting from the decomposition, in addition to physisorbed O-2, was attached to the aluminum ion constituting the Lewis sites. The oxygen molecules would then gradually be desorbed.