Isothermal decomposition of cubic ammonium perchlorate (AP) has been studied as a function of concentration of barium dopant by thermogravimetry in the temperature range 530-550 K. The rate of decomposition first passes through a minimum and then a maximum showing opposite effects, as the dopant concentration increases. The decomposition kinetics of both pure and doped AP was found to be best described by first order rate law with an activation energy (E) of ca. 138 kJ mol(-1). The results favour an electron-transfer mechanism.