TPD of pyridine desorbed from the surface of AlPO4-Al2O3 catalysts, with different Al2O3 loadings (5-15 wt%), yields a complex desorption curve consisting of three overlapped peaks which are ascribable to weak (T-m approximate to 460 K), medium (T-m approximate to 530 K) and strong (T-m approximate to 590 K) acid sites (Bronsted and Lewis). There is a homogeneous distribution of acid strength and an increase in alumina loading leads to an increase in the number of pyridine-adsorbing sites, even though there is no change in the strength distribution when catalysts are calcined at 773-1073 K. Furthermore, calcination at 1273 K reduces both the number and strength of the acid sites as the alumina content increases. The overall number of acid sites decreases continuously as the temperature of the pyridine adsorption increases.