Acidic properties of Re2O7/Al2O3 catalyst have been characterized by a combined study using Fourier transform infrared spectroscopy (FT-IR) and temperature-programed desorption (TPD). Pyridine was used as a base probe. The influences of reduction and the addition of alkaline salt to the catalyst have also been investigated. When the catalyst was reduced, strong acid sites decreased and weak acid sites increased. Significant differences in acidic properties were observed between 200 and 300 degrees C reduction temperature. The addition of an alkaline salt was very selective for destroying both the strong Lewis and Bronsted acid sites. CsOH poisned stronger acid sites more selectively. Good correlations between the FT-IR and TPD results were obtained for changes in acid strength and number of acid sites.