Mg-5Li-3Al-2Zn-xRE alloys were prepared. The microstructure and mechanical properties of as-cast and wrought specimens were studied. RE elements in Mg-5Li-3Al-2Zn alloy cause the microstructure refinement and the formation of Al3La, which bring about the improvement of mechanical properties of alloys. The optimal RE content for Mg-5Li-3Al-2Zn alloy is 2 wt%, which makes the microstructure the finest and the mechanical properties the best. The further increase of RE content makes the microstructure be coarsened and the morphology of Al3La change from particular to rod-like and pearlite-like eutectic shape, leading to the poor mechanical properties of alloys.