Magnesium based hydrogen storage nanomaterials, Mg-H and MgEr-H, were prepared through the DC arc plasma method followed by hydrogenation under high hydrogen pressure. The phase composition and dehydriding properties of the hydrogenated nanopowders were analyzed. It is revealed that Er addition can effectively increase the hydrogen absorption percentage of Mg powder and reduce the dehydriding temperature. The thermal decomposition behaviors of pure ammonium perchlorate (AP) and AP with the presence of the magnesium based hydrogen storage nanomaterials have been investigated by simultaneous thermal analysis (TG-DSC). The results show that both Mg-H and MgEr-H can promote the thermal decomposition of AP, including the low temperature reaction and the high temperature reaction. Particularly for the high temperature decomposition, the temperature can be decreased by 80 oC. The decomposition heat of AP is increased greatly, around twice of that of the pure AP, and the reaction rate is also much faster. Therefore, the magnesium based hydrogen storage nanomaterials with rare earth addition are good catalysts for the decomposition of AP