Bubble contamination in an ammonium perchlorate (AP)-based composite propellant has a positive effect on the burning rate. However, the quantative effect of the bubble contamination on the burning rate has never been revealed. In order to clarify the ralationship between the increase in the burning rate and the void fraction of the propellant, propellants were prepared with fine porous AP particled (PaAP) or fine hollow AP particles (HoAPs), and their burning rate characteristics were investigated. The voids inside AP particles have the effect of increasing the burning rate. The increase in the burning rate is enhanced linearly as the void fraction increases. The effect of the void fraction on the burning rate for a propellant containing PoAP is not identical with that for a propellant containing PoAP is not identical with that for a propellant containing HoAP. It was found that the effect of the void fraction on the burning rate could be estimated by the void fraction when the bubble contamination is uniform in size and shape.