Catalytic cracking of polypropylene has been carried out in a semibatch stirred reactor. The influence of the nature of the cracking catalyst and the reaction conditions on conversion and selectivity has been studied. Large pore zeolites as well as amorphous and ordered silica-aluminas have been used as catalysts, in order to better study the influence of pore size (micro and meso), crystallite size and the number and strength of the active acid sites. However, it is shown that from a practical point of view, the use of spent equilibrium catalyst from FCC units can be the most adequate solution.