We demonstrate a method to improve the promising hydrogen storage capabilities of ammonia borane by making composites with alkaline earth metal hydrides using ball milling technique The ball milling for the mixtures of alkaline earth metal hydride (MgH2 or CaH2) and ammonia borane (AB) yields a destabilization compared with the ingredient of the mixture, showing the hydrogen capacity of 8 7 and 5 8 mass% at easily accessible dehydrogenation peak temperatures of 78 and 72 C respectively without the unwanted by product borazine Through detailed analyses on the dehydrogenation performance of the composite at various ratios in the hydride and AB we proposed a different chemical activation mechanism from that in the LiH/AB and NaH/AB systems reported in a previous literature.