We show that some relevant parameters characterizing the surface thermodynamics of aluminosilicates can be obtained by using dielectric relaxation spectroscopy (DRS). The central assumption is that adsorption at the aluminosilicate surface is mainly related to the presence of extra-framework cations and, as a consequence, the activation barrier for cation displacement, measured from DRS, identifies the surface energy landscape. The modification induced by molecules adsorbed in the cation vicinity is therefore detectable via the evolution of the activation barrier. The methodology is applied to a typical test case: adsorption of water in two Na+-Mordenites characterized by two different Si/Al ratios. (c) 2006 Elsevier B.V. All rights reserved.