An attempt is made to form composites by mechanical alloying (MA) for the utilization of synergy effect to acquire both high capacity and ability to absorb/desorb protium at low temperatures. The composite has a well-bonded and uniform structure consisting of pure magnesium that has high hydrogen capacity up to 7.6mass% and LaNi5 alloy that is capable of protium absorption/desorption at relatively low temperatures. The maximum protium content of a specimen of the composite mechanically alloyed is 2.77mass% at 40 degreesC. Consequently, the result suggests the occurrence of synergy effect during the absorption process since the hydrogen capacity of LaNi5 is lower than 2.77mass% at 40 degreesC and magnesium cannot absorb at a relatively low temperature of 40 degreesC.