The degradation of polypropylene in the presence of solid catalysts of different acidity was studied by thermogravimetric analysis (TGA) employing three different heating rates. The temperatures of onset, T-on, of maximum-rate, T-max as well as of end, T-end, of the degradation shifted to lower values as higher the acidity of the catalysts. A comparison among the catalytic activities has been performed on the basis of the apparent kinetic parameters, frequency factor and activation energy, obtained from the TG data. The maximum activity was observed for the more acidic catalysts (silica-aluminas).