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 A13Zr 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