The microstructure and mechanical properties of 5A90 Al-Li alloy sheet joint by laser welding with filler wire (LWFW) have been studied. The results indicate that the major microstructure characteristics of the joint by LWFW are fine-grained layer and equiaxed grains in most of the welded seam, which are also the major characteristics of the joint by laser beam welding (LBW). However, compared with the joint by LBW, the microstructure of the joint by LWFW is finer, and the range of the columnar crystals zone is prone to decrease. The microhardness HV0.2 of welded seam by LWFW (925.7 MPa) is lower than that by LBW (956.5 MPa), but the uniformity of the former is better than that of the latter. The ultimate strength of the joint by LWFW is lower than that by LBW slightly, which reach to 73.03 % and 79.22% of the base metal, respectively, whereas the elongations after fracture of the former joint is higher than that of the latter joint significantly, which reach to 38.65 % and 20.38 % of the base metal, respectively. Form those results, the microstructure and mechanical properties of 5A90 Al-Li alloy by LWFW are better than that by LBW slightly. If the combined mechanical properties of the joint by LWFW meet the operation requirements, it should be improved by heat treatment after welding, and it also should develop a better filler wire matched with the base metal.