Pentaerythritoltetranitrate (PETN), Cyclotrimethylenetrinitramine (RDX), Cyclotetramethylenetetranitramine (HMX) are important high explosives used in a variety of military and industrial formulations. The present work investigates the interaction Ammonium Perchlorate with RDX, HMX and PETN and the effect of the interaction on the thermal decomposition of Ammonium Perchlorate. The microencapsulation of modified AP crystal was done with Viton. Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) were used to investigate the thermal properties and heat of decomposition. Kinetic analysis was done by Flynn Wall Ozawa (FWO) method. Scanning Electron Microscopy (SEM) was used to study the surface morphology of modified AP. The decomposition products were analysed by TG-MS. The presence of RDX/HMX/PETN or its decomposition products appears to catalyse the decomposition of AP.