HMS and Al-HMS materials with Si/Al ratio in the range 5–45 were synthesized by neutral templating pathway. The as synthesized as well as calcined samples were examined for pore size distribution, surface area and XRD. These investigations confirmed the hexagonal mesoporous structure formation at all Si/Al ratios. The TGA measurements indicated that two types of template species interacting with Si or Al could be distinguished. The acidity and acid strength distribution studies using microcalorimetric NH3 adsorption indicated that the acidity increases with Al content in the mesoporous structure. The presence of Al in the structure creates a wide variety of acid sites of varying strengths. The heterogeneity of the sites also increases with Al content of the catalysts. The activities for cumene cracking reaction to test acidity of the materials supported the trend obtained from microcalorimetric NH3 adsorption results. © 2006 Elsevier B.V. All rights reserved.