Although composite propellant has been studied for a long time, the role of density of the composite propellant has not been addressed adequately in the literature. This paper examines the role of density of the propellant with regards to burn rate and burn rate pressure index. Propellants were prepared in the four different size (15, 70, 200 and 1000 g) mixers with identical input of ingredients to examine the effect of mixer size on density and burn rate of the composite solid propellant. It is noticed that density of the propellant changes significantly with change in the mixer size from 15 g to 1000 g. This is because for the smaller mixers the surface area to volume ratio is large and the actual percentage of aluminum and ammonium perchlorate (especially coarse) that goes into the propellant reduces. High burn rate with decrease in mixer size is also accompanied with increase in burn rate pressure index. These high burn rate and burn rate pressure index with decrease in mixer size is because of larger fraction of coarse AP particles as compared to fine AP particles remaining attached to the mixer and decreases the coarse to fine AP ratio in the cured propellant. 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.