The effects of fuel particle size on the combustion propagation rate of the reverse combustion in a packed bed were studied experimentally. WE, used spherical pellets of activated carbon having a size range of 2.8-6.7 mm. Superficial air velocity was set in the range of 0.012-0.165 m/s. The experimental results showed that in the lower gas velocity region, the combustion front propagation rate increased with the air velocity independently of the particle size. However, at air velocity beyond a certain value, the propagation rate took an asymptotic value that increased with decrease in the particle size.