Nitrocellulose based (NC) and nitroglycerin based (NG) propellants often have a fixed acid and water content during the manufacturing time. After manufacture, the quantity and ratio of acid/water will continue to vary depending upon the conditions of storage and operation. The level of variation depends on many factors such as loading density, temperature, volume of ullage and sealing condition of the containing cartridge, just to name a few. As described in this paper and other literature, the degradation mechanisms and aging processes of NC/NG based propellants are extremely complicated. This paper describes the details of the application of Electron Spin Resonance (ESR) to study if the free-radical mechanism is involved in the decomposition of nitrocellulose and nitroglycerin. Due to the high free-radical intensity possessed by the propellant composition, we believe that a a complex intermediate may be formed between DPA and NG and/or NC. The formation of a it complex intermediate is not preferred because it may enhance the rate of decomposition of nitrate esters. Correlation between heat flow curve, stabilizer depletion and free-radical distribution has been evaluated. An intramolecular decomposition mechanism is preferred, because it prevents the possibility that the NOx from NNODPA or NNDPA may interact with the NC and NG again during the rearrangement process. Since the acidity of the propellant composition continues to change during the aging process, multiple mechanisms may proceed simultaneously.