AlCl3 has been successfully immobilized on MCM-41 mesoporous silica of different pore sizes to form a novel shape-selective catalyst for the Friedel-Crafts alkylation of benzene with long-chain olefins (linear 1-olefins with a chain length of 6 to 16 carbon atoms). The selectivity toward the monoalkylated product is strongly influenced by the pore size of the carrier material. This demonstrates the opportunities offered by the micelle-templating method to tailor shape-selective catalysts for reactions with bigger molecules.