The thermal decomposition of a high-energy oxidizer viz., guanylurea dinitramide (GUDN) has been studied by non-isothermal thermogravimetry (TG) and thermogravimetry combined with mass spectrometry (TG-MS). Isoconversional method of Vyazovkin (VZ) was used to investigate the dependence of activation energy (E-a) on conversion (alpha). A strong dependence of E-a on alpha, where the E-a increases steadily for up to an alpha of similar to 0.6 followed by a marginal increase and reaches similar to 435.0 kJ mol(-1) at the end of the reaction. E-a has also been determined for GUDN using Kissinger's method. A comparison of the results from Kissinger and isoconversional method shows that the activation energies from these methods are comparable. Using the model free isoconversional method, the isothermal conversion as a function of time at two different temperatures was also computed. The evolved gases during the decomposition of GUDN were analyzed by TG-MS which revealed the formation of ions corresponding to N-2, O-2, NH3, H2O, N-2, NO, methane diimine, isocyanic acid, N2O, NO2 and urea. (C) 2016 Elsevier B.V. All rights reserved.