Thermogravimetric analysis (TGA), coupled with Fourier transform infrared (FTIR) spectroscopy and mass spectrometry (MS), has been utilized to study the thermal decomposition of ammonium perchlorate (AP). The effect of sample size and that of confinement using a perforated lid on crucibles was studied. Kinetic parameters were extracted from TGA data using isoconversional methods and kinetic compensation effect. Among several interesting trends that emerged, the increase in the decomposition rates with increase in particle size, in the first phase the presence of NO among the gases detected only during the tests conducted in crucibles with a pierced lid (CPLs), and the activation energy for the tests conducted in CPLs being close to the activation energy of sublimation of AP, were the prominent ones. The species detected by FTIR spectroscopy were NH3, N2O, HCI, NO2, H2O, NO, and HNO3, while those detected by MS were Cl-2, O-2, HOCl, CIO, and NH(4)C1.