Decomposition mechanisms of propellants are of great interest in understanding performance issues of chemical propulsion systems. The characterization of physico-chemical properties of Glycidyl azide polymer (GAP), specifically deuterated analogs, was investigated in this study. The purpose of this new approach is to identify the key steps in thermal decomposition mechanism of GAP. The present work shows that the use of deuterated GAP is a good method to study the decomposition pathway of energetic polymers. The polymerization process was successful, but was nevertheless affected by the use of the isotopic monomer since the resulting polymers had a slightly lower molecular weight. The chemical characterization of the deuterated GAPs by NMR and FTIR confirm the structure of these new polymers. The TGA analyses show a larger weight loss during the first step of decomposition for labeled GAP suggesting that molecular nitrogen and heavier compounds are produced simultaneously.