Butt　joints　of　3.0　mm　thick　sheets　of　5A90　Al-Li　alloys　have　been　produced　using　Nd:YAG　laser　welding.　Grain　shapes　and　grain　orientations　in　the　horizontal　and　transversal　welds　were　studied　using　electron　back　scattered　diffraction　(EBSD).　The　results　show　that　a　narrow　band　of　non-dendritic　equiaxed　grain　zone　(EQZ)　is　formed　along　the　fusion　boundary.　The　weld　metals　exhibit　equiaxed　dendritic　microstructures　with　random　orientations.　The　non-epitaxial　growth　mode　occurs　in　the　weld　metal　grains,　which　does　not　follow　special　orientation　relationships　with　the　base　metal　grains　due　to　the　presence　of　the　EQZ.　The　equiaxed　dendritic　grains　are　resulted　from　heterogeneous　nucleation　aided　by　equilibrium　Al3Zr　phases　as　well　as　the　high　degree　of　constitutional　supercooling　occurring　in　the　advancing　solidification　front　of　welding　pool　during　the　solidification.　A　combination　of　the　chemical　compositions　of　5A90　Al-Li　alloys　and　Nd:YAG　laser　welding　processes　accelerate　heterogeneous　nucleation.