Catalytic dehydration of acetic acid was performed over surface-modified MCM-41. Calcination of silylated MCM-41 under air regenerated successfully silanol groups as the active sites for dehydration of acetic acid. In-situ FTIR spectroscopy using pyridine as a probe molecule revealed that as the pretreatment temperature before silylation increased, the concentration of Lewis-acidic sites was enhanced. The enhanced concentration of Lewis-acidic sites augmented the bridged adsorption species of acetic acid on the surface of the modified catalyst, which significantly promoted the catalytic activity.