The effect of LiBH4 on the hydrogen sorption performance of magnesium was investigated. It was found that the hydrogen storage properties of LiBH4/Mg mixtures exhibit a dramatic improvement as compared to plain magnesium powder. For example, at 250 C, a LiBH4/Mg (mass ratio 1:4) composite can absorb 6.7 wt % hydrogen in 60 min, while only less than 1 wt % hydrogen was absorbed by pure magnesium in the same period under similar conditions. The hydrogen desorption properties of the composite at 350 C were also improved significantly as compared to the plain magnesium powder. Furthermore, highly activated magnesium hydride was synthesized directly by ball milling LiBH4/Mg mixtures under high hydrogen pressure. The synthesized magnesium hydride exhibits superior kinetics, absorbing 5.78 wt % hydrogen at the relatively low temperature of 200 C within 100 min.