The thermo-mechanical effect on combustion behavior of incorporating inert impurity particles into double-base propellants is investigated. Burning rate and temperature profile measurements of propellants containing various amounts of aluminium oxide powders of different grain sizes indicate that the inclusion of inert impurity particles enhances the burning rate at low pressures, the effect diminishing with increase in pressure. A theoretical model is constructed, based on the assumption that the interfaces created by these particles provide internal burning surfaces which decompose following an Arrhenius relationship. The simple theoretical model predicts the trend of the experimental results, but cannot provide any insight into the contribution of the thermo-mechanical effect to the overall heat of condensed phase reaction in double-base propellants.