The effects of Mg addition content and ball milling time on the hydrolysis kinetics of MgH2 prepared by hydriding combustion synthesis (HCS) in MgCl2 solution were investigated. When MgH2-60%Mg was milled for 3 h, hydrogen yield reached to 993 mL/g within 5 min (80% in conversion) and the hydrolysis was completed within 15 min with a single phase of Mg(OH)2 as the byproduct. Results indicate that the HCSed MgH2 with addition of Mg can serve as a low-cost on-board hydrogen source with some advantages such as excellent kinetics of hydrolysis and easy recycle of byproduct.