To obtain magnesium alloys with a low density and improved mechanical properties, Y element was added into Mg-4Li-3Al (wt.%) alloys, and the effect of Y content on microstructure evolution and mechanical properties was investigated by using optical microscopy, scanning electron microscopy and tensile tests. The results show that mechanical properties of as-cast Mg-4Li-3Al alloys with Y addition are significantly improved as a result of hot extrusion. The best comprehensive mechanical properties are obtained in hot-extruded Mg-4Li-3Al-1.5Y alloy, which possesses high ultimate tensile strength (UTS=248？MPa) and elongation (δ=27%). The improvement of mechanical properties of hot-extruded Mg-4Li-3Al-1.5Y alloy was mainly attributed to combined effects of grain refinement, solid solution strengthening and precipitation strengthening.