In an attempt to determine the aging behavior of hydroxyl-terminated polybutadiene-based composite solid propellants, viscoelastic measurements were used to study the effect of thermal aging on this kind of energetic material. Accelerated-aging tests at 40, 60, and 80degreesC were performed for 5000 h. The changes in the dynamic mechanical properties, including the storage modulus (E') and loss factor or damping efficiency (tan 8), with time and temperature were measured to determine the aging rate and likely mechanisms occurring during this process. An Arrhenius analysis based on the determination of relative rate constants showed a linear tendency from tan 8 values, whereas a significant curvature was found from E' values. In addition, the effects of external (surface) and internal (core) sampling in the intensification of the aging process were analyzed. The results confirmed dynamic mechanical analysis as a powerful tool for determining the aging characteristics of composite propellants. This technique allows the evaluation of the actual state of a propellant grain with a small sample and a straightforward measurement. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2397-2405, 2003.