The life time analysis of energetic liquid prepolymers, polyglycidyl azide (PGA), and its precursor, polyepichlorohydrin (PECH), was carried out to estimate their useful storage time as a function of storage temperature using thermoanalytical method. Thermogravimetric Analysis (TGA) was used to determine the decomposition kinetics of prepolymers. For this purpose, Thermal Gravimetry (TG) curves of prepolymers were recorded at different heating rates and their kinetic activation energies were determined. The kinetic activation energy of PGA and PECH were found to be 120 and 167 kJ/mole, respectively. For the life time estimation, the 5% weight-loss was selected as constant failure criterion for the prepolyemers. These data were further used for the determination of the change in their useful storage time at different storage temperatures.