Thermal ageing of hydroxyl-terminated polybutadiene propellant binders was carried out at various temperatures between 50 and 100-degrees-C. The changes caused by this treatment in properties such as melt viscosity, functional end-groups, molecular weight, tensile strength, elastic modulus and ultimate elongation were examined. The viscosity and average molecular weight increased with the ageing temperature and ageing period. A decrease in ultimate elongation and an increase in elastic modulus were observed. Tensile strength of the matrices prepared by curing hydroxyl-terminated polybutadiene with isophorone diisocyanate did not change. Lifetime for usability was predicted from the application of the Arrhenius equation to be 7 years.