The microstructure and mechanical properties of as-cast, solution-treated and as-extruded Mg-8Li-4Al-0.3Y alloys were studied by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction analysis (XRD) and tensile tests machines, etc. The results show that as-cast Mg-8Li-4Al-0.3Y alloys are composed of ɑ-Mg, β-Li, Al2Y, AlLi and MgAlLi2 phases. MgAlLi2 compound and most of AlLi phase decomposes and dissolves into the matrix, only part of larger AlLi particles are left during the solution treatment. The micro-hardness of solution-treated alloy is much higher than that of as-cast one due to solution strengthening. The mechanical properties of Mg-8Li-4Al-0.3Y alloys are improved a lot by extrusion and the ultimate strength and elongation of the extrude alloy reaches to 208 MPa and 25.1% respectively.