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.