The effect of Sn addition on the microstructures and mechanical properties of Mg-5Al-2Si alloys was investi- gated with variations of Sn contents (3 and 6 wt pct). The microstructure of the alloy was characterized by the presence of Mg2Sn particles within matrix and at grain boundaries. As the Sn contents increased, yield and ultimate tensile strength were increased at room temperatures and 150℃. Creep properties were improved with the increasing amount of Sn due to the fine precipitation of Mg2Sn phases within grain during creep.