The energetic plasticizers like azidopolyester (APE) in Hydroxy Terminated Poly-Butadiene (HTPB) binder formulations are known to enhance the ballistic properties of explosive formulations. The pyrolysis gas chromatography-mass spectrometry (Py-GCMS) studies were carried out on HTPB with APE to get insight of the decomposition pathway of HTPB. Based on the results, decomposition mechanism is proposed for uncured and cured HTPB, with and without energetic plasticizer. It has been observed that the decomposition mechanism of cured HTPB is similar to the pure HTPB polymer. In case of energetic plasticizer based composition, it is seen that APE triggers the decomposition which results in the formation of monomers, dimer and oligomers. Overall, the study helps in understanding the role of energetic plasticizer on improving the performance of the binder composition