Thermal degradation profile of hydroxyterminated polybutadiene (HTPB)-based polyurethane and polyurethaneureas has been studied as function of chain extender concentration. Thermogravimetric analysis revealed the degradation as a two-step weight loss process. The cross-link density of polyurethane was seen to restrict the extent of weight loss during the depolycondensation of urethane bonds at higher temperature. Degradation in polybutadiene segment was associated with fragmentation, cyclization followed by rapid chain scission. Polyurethanes experienced a lower weight loss in first step during thermo-oxidative degradation over that in presence of nitrogen. The step-wise activation energies of degradation were calculated by Coats-Redfern and Chatterjee-Conrad methods. Accelerated aging of polyurethanes in air results in lowering of tensile strength with time.