In this work，the microstructure evolution and mechanical properties of Mg-12Gd-1Zn-0.5Zr-0.5Ag (in wt.%) alloys with different contents of Al and Li elements by T6 heat treatment were investigated. The results indicate that new Mg3Gd particles are precipitated in Mg-12Gd-1Zn-0.5Zr-0.5Ag alloy and most Al2Li3 phases in Mg-12Gd-4Al-3Li-1Zn-0.5Zr-0.5Ag and Mg-12Gd-6Al-5Li-1Zn-0.5Zr-0.5Ag alloys become smaller and more evenly distributed after T6 heat treatment. The grain size and c/a ratio values of the as-aged Mg-12Gd-4Al-3Li-1Zn-0.5Zr-0.5Ag alloy and Mg-12Gd-6Al-5Li-1Zn-0.5Zr-0.5Ag alloy are decreased significantly than that of as-aged Mg-12Gd-1Zn-0.5Zr-0.5Ag alloy, which results in improved tensile strength and plasticity. The best combination of tensile strength, elastic modulus and plasticity is as-aged Mg-12Gd-6Al-5Li-1Zn-0.5Zr-0.5Ag alloy, the ultimate tensile strength, modulus and ductility are 210 MPa, 50.7 GPa and 24.8%, respectively.