Grafting of AlCl3 onto Si-MCM-41 using the reaction of anhydrous AlCl3 from its CCl4 solution with terminal Si-OH groups of Si-MCM-41 under reflux at two different concentrations of AlCl3 relative to Si-MCM-41 has been studied. The influence of thermal-treatment conditions (viz., temperature and gas atmosphere, such as vacuum, static or flowing air, and flowing N-2) on bulk and surface properties of the AlCl3-grafted Si-MCM-41 has also been investigated. The AlCl3-grafted Si-MCM-41 samples before and a er thermal treatment were characterized by Fourier transform infrared, Al-27 magic-angle spinning nuclear magnetic resonance, Xray photoelectron spectroscopy, and energy disperse X-ray analysis (EDAX) analysis and also for their surface area and concentration of strong acid sites (measured in terms of the pyridine chemisorbed at 400degreesC). The incorporation of tetrahedral Al in the MCM-41 structure with the creation of strong acid sites could be accomplished by thermally treating the AlCl3-grafted Si-MCM-41, particularly in a flow of N-2 at 400 degreesC.