Welding of 1420 aluminum-lithium alloy has been investigated using a high power YAG Laser. The results show that the threshold for penetration welding of 1420 Al-Li alloy is about 1.2×106 W/cm2, lower than those of the traditional Al alloys. Pores, which are the main welding defects, mainly locate near the bond line. Tensile test shows that the weld near the bond line is the weakest part of the joint.