AbstractFine porous ammonium perchlorate (PAP) has small holes in its crust, and the voids in the particles are connected to the outside. The porosity of PAP results in fine bubble contamination in a propellant because the voids in PAP cannot be completely charged with a binder. Fine bubble contamination can improve the burning rate characteristics of an ammonium perchlorate (AP) propellant. The influence of the porosity of PAP on the burning characteristics of an ammonium nitrate (AN)/AP propellant and the effect of Fe2O3 as a catalyst on them were investigated in this study. The void fraction of the propellant increased with increasing mass ratio between AP and all oxidizers (ξ) and ranged from 1.3 % to 3.2 %. The porosity of PAP increased the burning rate of AN/AP propellants. This effect increased with decreasing pressure and was independent of ξ. However, porosity had minimal influence on the burning rate of AN/AP propellants with Fe2O3. The effect of the catalyst on the increase in the burning rate due to the porosity of PAP was influenced by pressure and ξ. The effect on the AN/AP propellant was greatest when ξ was in the 0.5–0.6 range.