Abstract: The microstructure and mechanical properties of MLZ91 Mg-Li alloy laser welded joints were studied by using optical microscope, scanning electron microscope, tensile equipment and hardness tester. The results show that the rapid melting and solidification process of laser welding can significantly refine the coarse lathe α +β duplex structure of MLZ91base metal; due to the fine grain strengthening of the weld, the disappearance of the over-aging softening phase θ, and the dispersion strengthening of the fine and uniformly distributed precipitates, the mechanical properties of the butt joint weld are better than that of MLZ91 base metal;the shear resistance of lap joints is proportional to the effective connection size of lap surface.