The Mg-0.5%Zn-0.5%Zr-RE alloy was prepared by extrusion and then T5 and T6 heat-treatments were carried out. The tensile mechanical properties were tested. Results indicate that the yield strength of the alloy in T6 state is a little lower than that in T5 state. The tensile strength of the alloy at T6 state is 313 MPa, higher than 289.5 MPa in T5 state. OM observation indicates that the T5 alloy remains the extruded microstructure. TEM results show that the strengthening of Mg-0.5%Zn-0.5%Zr-2.2%Nd-4.0%Y in T6 state originates from the precipitation of β″ and β′ and the interaction of dislocation. The precipitation order of Mg-0.5%Zn-0.5%Zr-2.2%Nd-4.0%Y alloy is SSSS→β″→β′→β under 520 oC, 2 h solution + 200 oC aging