Flame spreading rate over the unburnt surface and burning rate of composite solid propellants are determined experimentally. Tests are conducted in the pressure range of 0.5 to 5 bar with propellants containing two different aluminium content using window bomb facility. The influence of various sample orientations on flame spreading rate and the convective flow of hot burnt gases has been studied. Combustion photography is used to determine the flame spreading rate and burning rate of propellants through image processing technique. Similar to earlier studies, the phenomenon of secondary ignition is observed over the unburnt propellant surface, towards vertical spread case when the flame propagation occurs in upward direction. Flame spreading rate is distinctly higher than burning rate in the tested pressure range, irrespective of the aluminium content in propellants. High content of aluminium in propellants results in larger increment in flame spreading rate over burning rates, when compared to the one with less aluminium. This study could be extended to more complex situations, which incorporates the combined effect of pressure, forced convection and radiative heat transfer on the flame spreading rate. © Asia-Pacific Conference on Combustion, ASPACC 2019.All right reserved.