The acid properties of sulfated alumina, titania and zirconia have been characterised and these solids compared in the isomerisation of alpha -pinene oxide in the liquid phase at 273 K. This comparison shows that the:formation of campholenic aldehyde requires a mild Lewis acid. Only sulfated alumina is a good catalyst giving yields reaching 76% at full conversion in less than 1 h, though with a relatively high catalyst : reactant ratio. The conditions of preparation of this solid show a significant influence on the acid properties and therefore on the catalytic properties of the resulting solid. The best results are obtained with sulfated alumina prepared with a ratio of hydrolysis of 1 and an activation temperature of about 923 K.