Laser oscillating welding technology was applied to 2219-T651 aluminum alloy under different oscillating frequency and amplitude. The corresponding relationships between the oscillating parameters, the weld porosity, the joints formation, the microstructures and properties of the welded joints were revealed. The results show that compared with laser welding, laser oscillating welding can reduce weld porosity. When oscillating amplitude is set at 2.5 mm, the weld porosity can be decreased to 1.66%. In comparison with base metal, the heat-affected zone and the fusion zone are softened. Due to the weakening of the precipitation strengthening effect, the microhardness in the heat-affected zone near the weld gradually decreases until a “platform” appears. Meanwhile, the fusion zone is composed of α(Al) matrix, α(Al) + θ(Al2
Cu) eutectic phase distributed between dendrites and grain boundaries. Because of the diminished solid solution strengthening effect caused by Cu segregation, the microhardness in the fusion remain the lowest. Additionally, the grain sizes of the welds are refined under some oscillating parameters, leading to slight increase in the microhardness. The tensile strength of the welded joint reach the highest 318 MPa under the oscillating frequency of 150 Hz and the oscillating amplitude of 2.5 mm, which is approximately 69.4% of that of the base metal. The tensile strength of the welded joint shows negative linear correlation for the area proportion of fracture pores. The weld porosity is the main factor to affect the tensile strength of the welded joint.