This paper studies the effects of ageing on the mechanical properties of an AP-Al-HTPB based composite solid propellant. A novel accelerated artificial aging method has been proposed which accounts for temperature fluctuations as the main contributor. The scheme establishes a relation between the natural ageing of full size propellant grain and the artificial ageing of a specimen in a laboratory. The relation has been achieved by solving heat diffusion equation under ambient temperature fluctuation conditions. A comparison has been made between the mechanical properties of a naturally aged propellant (4 years old) and a fresh batch of the propellant of the same composition. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.