Sulfonic acid functionalized mesoporous ZSM-5 (SO3H-Meso ZSM-5) were prepared by post-grafting of 3-mercaptopropyltriethoxysilane with various loading in the range of 10-50 wt% followed by oxidation of thiol using H2O2 to generate the corresponding sulfonic acid group. Grafting of organic moieties was evidenced by elemental analysis, Si-29 & C-13-NMR and X-ray photoelectron spectroscopy. The SO3H-Meso ZSM-5 catalyst with improved acidity and mesoporosity exhibited enhanced catalytic activity in acid-catalyzed liquid-phase reaction of 2'-hydroxyacetophenone and benzaldehyde compared with nonfunctionalized mesoporous ZSM-5 (Meso ZSM-5) and functionalized microporous ZSM-5 (SO3H-ZSM-5). The higher loading of sulfonic acid functional groups led to higher acidity and consequently resulted in higher yield of products. The catalyst could be reused up to three cycles without significant loss in its catalytic activity. (C) 2014 Elsevier B.V. All rights reserved.