Magnesium (Mg) has been paid attention to the viewpoint of weight reduction of structural materials. However, Mg alloys fabricated by the ingot metallurgy process have limited applications as structural materials due to their low mechanical property and low corrosion resistance. In this research, novel Mg-Al alloy was synthesized by the mechanical alloying-spark plasma sintering (MA-SPS) process. Vickers hardness test and X-ray diffraction were carried out to evaluate the effect of Al addition on the properties of the Mg-Al alloys. The hardness improved with increasing amount of Al, in particular when 30 mass% Al was added, the value of hardness was over 200 HV. This improvement was attributable to Mg17Al12 identified by X-ray diffraction. In conclusion, hardness of Mg were improved by the addition of Al via the MA-SPS process.