In the present work, the synthesis of silica-alumina-pillared montmorillonites and their structure are studied. Hydroxy-silico-aluminum oligocations have been obtained by treating previously synthesised aluminum polycations with Si(OC2H5)(4). Several Si/Al ratios (0, 0.5, 1, and 2) have been used to prepare pillared clays with various microporous accessibility and acidic properties. The Study of the fractal dimensions of the solids shows that their Surface becomes more heterogeneous after pillaring. The acidity of alumina- and silica-alumina-pillared montmorillonites is mainly of the Lewis type, and the nature of the acid sites detected by pyridine adsorption seems to be independent of the Si/Al ratio. These results are Supported by the product distribution obtained in the 1-butanol dehydration reaction. (C) 2004 Elsevier Inc. All rights reserved.