Carboxyl-terminated polybutadiene (CTPB) was subjected to temperature and humidity aging in order to estimate its useful lifetime as a solid propellant binder. CTPB samples were temperature aged from 1 week to 7 months at various temperatures ranging from 50 to 100°C. At various stages of temperature aging, viscosity of the samples were measured, end group analyses were performed, and the samples, after being crosslinked with MAPO, were mechanically tested. As far as mechanical properties are concerned, the ultimate tensile stress of the samples decreases with temperature aging and strain at break increases. End group analyses indicate that acid value of the samples decreases with aging and viscosity increases. The results of temperature aging were applied to an Arrhenius type time-temperature superposition relation and useful lifetime of CTPB as binder at 20°C was predicted to be around 10 years. The CTPB samples were also humidity-aged and the effects of humidity aging on mechanical properties were investigated. The results indicate that similar to temperature aging, ultimate tensile strength decreases and strain at break increases with aging. The effects of humidity aging, however, is much less pronounced in comparison to temperature aging.