The rearrangement of isophorone oxide over Al-MCM-41-type mesostructured catalysts with different Si/Al molar ratios was investigated. The main rearrangement products were the alpha-diketone and the keto aldehyde, whereas the product coming from the decarbonylation of the latter was detected in minor amounts. The textural properties and the number of acid sites of Al-MCM-41 materials influence the extent of isophorone oxide rearrangement reaction. The best catalytic performance in terms of epoxide conversion was obtained for a catalyst with a molar Si/Al ratio around 40 due to the proper contribution of acid site concentration and pore size. However, irrespective of the aluminium content of the catalysts and the reaction temperature, the selectivity to the desired keto aldehyde was around 80%. Al-MCM-41 materials are superior catalysts compared with zeolites in terms of both activity and aldehyde selectivity. Because of their large pore size, using Al-containing mesostructured materials as catalysts in isophorone oxide rearrangement avoids the diffusional problems present in zeolites. (c) 2005 Elsevier Inc. All rights reserved.