We have investigated about age hardening behavior in Mg-1.5at%Sn system with additional elements. During the artificial aging at 150°C, solid solutionized Mg-1.5at% Sn alloy undergo the precipitation of superstructured intermediate phase after precipitation of GP zone. This intermediate phase triggers the increment of hardness value. Peak hardness is obtained when intermediated phase and fine equilibrium Mg2Sn phase coexist together. Although addition of third elements (Si and Zr) does affect the aging kinetics, the absolute hardness value is increased.