This is a study of the thermal decomposition of hexahydro-1,3,5-trinitro-1,3,5-triazine or cyclotrimethy-lenetrinitramine (RDX) nanoparticles by simultaneous thermo-gravimetry differential thermal analysis (TGA/DTA) and differential scanning calorimetry (DSC) under nonisothermal conditions, at various heating rates from 5 to 20 degrees C min(-1). The influence of particle size on the thermal decomposition was verified. The activation energy for the decomposition of each sample was calculated using the peak temperature shift method, proposed by Kissinger and Ozawa. A significant variation in varying particle observed the results size of RDX. The results showed that, as the particle size of RDX is increased the thermal decomposition temperature of RDX and its decomposition activation energy are enhanced. The values of activation energy obtained by the Kissinger and Ozawa methods for RDX samples with various particle sizes show that the activation energy for micron sized RDX is 1.5 times higher than that for nano-RDX. The values of Delta S-#, Delta H-# and Delta G(#) of decomposition reaction for each particle size were also computed. Base on the kinetic data, the relative sensitivity of RDX samples was found in the order: 180 nm RDX > 250 nm RDX > 300 nm RDX > 50 mu m RDX. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.