In　this　study,　the　joint　of　novel　Al-Mg-Zn-Er-Zr　alloy　were　performed　by　using　metal　inert　gas　(MIG)　welding　with　ER5E61　filler　wires.　The　mechanical　properties　and　corresponding　microstructure　of　the　base　metal　(BM),　heat-affected　zone　(HAZ)　and　weld　metal　(WM)　were　investigated.　The　MIG　welded　joint　in　Al-Mg-Zn-Er-Zr　alloy　achieves　an　ultimate　tensile　strength　(UTS)　of　337.5　MPa,　with　a　high　strength　coefficient　of　0.81.　The　UTS　values　for　the　BM,　HAZ,　and　WM　are　420.5　MPa,　376.3　MPa,　and　339.6　MPa,　respectively.　Compared　to　the　BM,　the　joint　strength　is　reduced,　indicating　the　occurrence　of　joint　softening.　The　reduced　mechanical　properties　in　the　HAZ　are　primarily　attributed　to　the　coarsening　of　Al6Mn　and　Al3(Er,　Zr)　nanophases　and　the　decreased　dislocation　density.　Fracture　analysis　reveals　that　the　WM　is　the　weakest　region　in　the　joints,　characterized　by　the　complete　dissolution　of　Mg32(Al,　Zn)49,　Al6Mn,　and　Al3(Er,　Zr)　nanophases,　a　reduced　dislocation　density　of　0.99　×　10　¹⁵　m⁻²,　and　a　lowered　Mg　content　of　5.09　wt%.　The　softening　of　WM　is　considerably　compensated　by　using　the　filler　wires　with　higher　Mg　content,　leading　to　the　elevated　strength　efficiency.　©　2025