Gallium containing SBA-15 mesoporous materials with different Si/Ga ratio were synthesized using an in situ sol-gel procedure with an aqueous solution of Ga(NO3)(3). The materials were characterised by means of elemental analysis, BET, XRD, TEM, and H/D isotope exchange techniques. It appears that depending their loading, stable Ga-species were either anchored to the siliceous matrix of SBA-15 or introduced in the framework via isomorphous substitution, thus generating acid properties in their host material. The catalytic activity of Ga-SBA-15 materials has been evaluated in the Friedel-Crafts acylation of anisole with benzoyl chloride and in the alkylation of benzene using benzyl chloride as alkylating agent. The activity of these catalysts was compared with the one of Ga-modified SBA-15 by post-treatment. A complete conversion of benzyl chloride over Ga-SBA-15 materials has been reached after 3 It of reaction with a 75% selectivity toward diphenylmethane. In contrast to Ga-samples prepared by post-treatment, in situ Ga-SBA-15 present a lower stability in the acylation reaction. However, the catalytic results indicate that Ga-SBA-15 mesoporous materials can be used as versatile and stable acid catalysts for Friedel-Crafts reactions with appropriate behavior depending on their preparation mode. (c) 2006 Elsevier B.V. All rights reserved.