Abstract: Effects of Cu on microstructures and mechanical properties of laser-MIG hybrid welded joint of SYG960E ultra-high strength steel to 6061 aluminum were studied. The experimental results showed that compared with MIG welding, laser-MIG hybrid welding was beneficial to improve the weld appearance and welding quality. The interface layer of steel and aluminum has a double-layer structure consisting of needle-like FeAl₃ intermetallic compound at aluminum side and strip-like Fe₂Al₅ intermetallic compound at steel side. The Cu has great effect on the interface layer and mechanical properties of steel-Al joints. When the Cu is added, the thickness of interface layer, the crack sensitivity and maximum micro-hardness of steel-Al joints will be decreased, and the tensile strength of steel-Al joints will be increased by 110%. It is related to that Cu can restrain the growth of interface layer and decrease the brittleness of Fe-Al intermetallic compounds in the interface layer. Therefore, the addition Cu is an effective way to improve the microstructures and mechanical properties of laser-MIG hybrid welded joints of ultra-high strength steel to aluminum.