The effect of KMnO4, Fe23, CuO and copper chromite on the pressure limits of combustion of ammonium perchlorate was investigated. The lower pressure limit in all cases increased with small additions of each catalyst and then decreased at higher concentrations of catalyst. An upper pressure limit was observed in the deflagration of samples with high concentrations of KMnO4. It was further observed that the effect of catalysts depends strongly on the way they are distributed as well as their concentration. The catalysis were found to be much more effective at a smaller particle size.