The compositions, the gas properties in motor chamber and the aluminum oxide (Al2O3) particle size for two kinds of solid propellants with approximately 20% aluminum powder have been investigated. The SEM photographs of Al2O3 taken from nozzle entrance liner show that the aluminized PCP propellant with 47% volumetric fraction AP/HNIW and bimodal oxidizer 200-5 μm can offer greater possibility for increasing aluminum agglomeration than the aluminized HTPB propellant with 64% volumetric fraction AP and trimodal oxidizer 400-200-6 μm. The nozzle entrance liner of solid rocket motor with the PCP propellant shows greater erosion at 4 circumferential sections in line with grain slots due to the impingement of large particles, but that with the HTPB propellant shows uniform erosion with circumferential angle.