The influence of dealumination of two commercial amorphous silica-aluminas (ASAs) with acetylacetone on their textural properties, acidity and catalytic activity was studied by N2-sorption, NH3-TPD, FTIR of adsorbed pyridine as well as 1 H and 27 Al MAS NMR. Acetylacetone treatment increases the pore volume and surface area (+20+30%) of commercial ASA without changing the pore size. More than half of the Al species are extracted from ASA but the total acidity is preserved or even slightly increased (for the ASA with higher Al content). The percentage of acidic Al is increased by a factor 2. Dealumination results in a better access to acid sites and an increase of medium Brønsted acid sites (BAS), leading to a 1.5 higher catalytic activity for 3,3-Dimethyl-1-butene (33DMB1) isomerization.