Apparent activation energies of MgH2 hydrolysis in deionized water were deduced for the first time being 58.06 kJ/mol. This paper also reports the mechanisms of MgH2 hydrolysis and the effects of NH4Cl on the kinetics of magnesium hydride hydrolysis. Experimental results show that hydrogen generation via MgH2 hydrolysis exhibited the highest rates in 4.50 wt% NH4Cl solution. This is because addition of NH4Cl could effectively decrease the compactness of magnesium hydroxide. It is also found that addition of NH4Cl could effectively enhance the hydrolysis kinetics and lead to a reduction of the apparent activation energy of MgH2 hydrolysis. The apparent activation energies of MgH2 hydrolysis decreased from 58.06 kJ/mol in deionized water to 50.86 and 30.37 kJ/mol in 0.5 and 4.5 wt% NH4Cl solutions, respectively. MgH2-4.5 wt% NH4Cl system showed the fastest hydrolysis rate, producing 1310 mL e hydrogen in 5 min, 1604 mL g(-1) hydrogen in 10 min, and 1660 mL e hydrogen in 30 min at 60 degrees C. The results reveal that NH4Cl may be a promising reagent for promoting the hydrolysis of MgH2 for hydrogen generation systems, which demonstrated a new method to improve the hydrolysis of MgH2. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.