CO2 laser beam was used to weld 2519-T87 high strength aluminum alloy, and the microstructure and mechanical properties of the welds were studied and compared with the melting electrode inert gas (MIG) welds. Results indicate that the grains in laser welds are very fine, and the eutectic phase distributes more uniformly. After aging treatment, there are lots of finer θ′ phase in laser welds. And there is no equiaxed grain zone along the laser weld fusion line. Whereas the grains in MIG welds are coarser. The eutectic phase is strip morphology and network distributes along the grain boundary. After aging treatment, the size of θ′ phase is big and number of θ′ phase is small, and it does not distribute uniformly in the grains. There is a wide equaixed grain zone along the fusion line. The tensile strength of the laser weld after aging treatment can reach 74% of that of the base metal, whereas the tensile strength of MIG weld is only 61% of that of the base metal. And there is no softened zone in the heat affected zone (HAZ) of laser welds.