Thermal decomposition of poly(glycidyl azide) (PGA) has been studied by using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and high-temperature FTIR spectrometry. By using DSC and TGA techniques, the first stage weight loss of PGA due to exothermic decomposition of pendant azide (- N-3) groups was explained in terms of the energy released at every stage of decomposition. From the glass transition temperature (T-g) measurements, it was observed that T-g, values of PGA increased with increasing quantity of decomposed - N-3 groups. The course of the decomposition reaction was also studied by taking successive FTIR spectra. It was observed that during the first stage weight loss process of PGA, the main chain was not decomposed thermally; inter- and intramolecular linking reactions accompanied the side chain decompositions.