The ammonia IRMS-TPD (infrared-mass spectroscopy/temperature-programmed desorption) method was applied to sulfated zirconia in order to measure the acidic properties [number, strength and type (Bronsted or Lewis) of acid site]. Because the TPD profile was broad, the acid strength distribution was calculated by means of a simulation method on the basis of theoretical equations. The Bronsted acid strength distribution changed according to the calcination temperature of zirconia support. The presence of strong Bronsted acid site on samples prepared by an equilibrium adsorption of H2SO4 was in agreement with the high catalytic activity of these samples for reaction (mainly cracking) of heptane. (C) 2008 Elsevier B.V. All rights reserved.