Magnesium Metal Matrix Composites have been receiving attention in recent years as an attractive choice for aerospace, automotive and structural applications, because of their low density and superior specific properties. In the present experimental investigation magnesium based metal matrix composites were prepared by stir casting route. The composite was prepared by reinforcing 50 nm alumina nanoparticle so that the final composite contains 5, 10 and 15 wt.% alumina. Mechanical properties and hardness were evaluated. Significant improvement was observed in impact strength and hardness value.