Energetic thermoplastic elastomers (ETPEs) are futuristic binders for propellant/explosive formulations. Poly(glycidyl nitrate) (PGN)-based ETPEs have excellent performance, including a high energy and high oxygen content. PGN-based ETPEs were synthesized on PGN as a soft segment and hexamethylene diisocyanate extended 1,4-butanediol as a hard segment by a prepolymerization method. The thermal behavior of the PGN-based ETPEs was investigated by thermogravimetric analysis (TGA) and derivative thermogravimetry. A fitting strategy was adopted to study every stage of decomposition. The results show that the ETPEs had four main decomposition processes, and the peaks of each stage were at 212, 262, 322, and 414°C. The gas products were tested by TGA/Fourier transform infrared spectroscopy/mass spectrometry, and the main gas products of the samples were N2O, CH2O, C2H4O, and CO2. The previous results indicate the proposed mechanism of thermal decomposition. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40965.