The thermal decomposition of ammonium perchlorate has been studied using thermogravimetric analysis (TGA), coupled with Fourier transform infrared (FTIR) spectroscopy and electron ionization (El) mass spectrometry (MS) of the evolved gases. The thermal decomposition could be demarcated into three distinct regimes, the low temperature decomposition (LTD) regime and the high temperature decomposition (HTD) regime, with an intermediate regime between the two, named as the intermediate temperature decomposition (ITD) regime. Using FTIR spectroscopy, N2O was detected as the primary species during the LTD regime, followed by HCl, NO2, and HNO3, in lesser quantities. On the contrary, NO2 was found to be the principal species, followed by almost equal concentrations of HCl, N2O, and HNO3 in the HTD regime. Other important species, such as H2O, Cl-2, O-2, etc., although observed by MS, were not quantified. NO could not be identified in appreciable quantities in any of the regimes. Based on the species detected during the present work, and previous research, a reaction scheme has been proposed for AP decomposition in the LTD and the HTD regimes. (C) 2015 Elsevier B.V. All rights reserved.