The possibility of hydrogen generation by hydrolysis of magnesium borohydride and its ammoniates was explored. Results show that catalyst-free Mg(BH ) can generate 1700 mL (H )·g in 1 min, 2760 mL (H )·g in 2 h, and 3004 mL (H )·g in 5 h without any diborane (B H ) emission. Mg(BH ) presents the highest hydrogen yield reported to date. However, the hydrogen generation rate of Mg(BH ) may be too fast to be controllable in some hydrogen production cases. Therefore, NH was added to form ammoniates to further regulate the hydrogen supply kinetics of Mg(BH ) . The hydrogen yields of Mg(BH ) ·0.5NH , Mg(BH ) ·NH , Mg(BH ) ·2NH , Mg(BH ) ·3NH and Mg(BH ) ·6NH are 2376, 2029, 1780, 1665 and 1180 mL (H ) g , respectively, which demonstrates a well-controlled hydrogen supply rate. These results indicate that catalyst-free Mg(BH ) and its ammoniates have good hydrolysis performance and show promise as convenient high-density hydrogen generation materials.