This paper represented the effect of welding wires on microstructure and mechanical properties of 2A12 aluminum alloy in CO2 laser-metal inter gas (MIG) hybrid welding. Plates of 2A12 aluminum alloy were welded by ER4043 and ER2319 welding wires, respectively. Full penetration joints without any defects were produced. The X-ray diffraction was used to analyze the phase composition, while the scanning electron microscopy (SEM) was conducted to study the microstructure, segregation behaviors of major alloying elements and the eutectics formed at dendrite boundaries in the joints. The results showed that silicon and copper were concentrated at the dendrite boundaries and alpha-Al + Si + Al2Cu + Mg2Si eutectic was formed if the ER4043 welding wire was used. However, only copper was concentrated at the dendrite boundaries and alpha-Al + theta eutectic was formed by ER2319 welding wire. Finally, the tensile tests were performed and the fracture surfaces were analyzed. The results showed that the joint efficiency by ER2319 and ER4043 welding wires reached up to 78% and 69%, respectively. Coarse dimples and voids had been observed in the fractographs. The joints showed a transgranular type failure. (C) 2009 Elsevier B. V. All rights reserved.