The microstructure characteristics and mechanical properties of double-sided laser beam welded aluminum alloy T-joints for aircraft fuselage panels are systematically analyed. The experimental results show that five distinct zones are identified between the fusion zone center and the base material which consists cellular dendrite zone, parallel dendrite zone, partially melted zone, over-aged zone, and base material. The heat affected zone of the skin side is the weakest area. The tensile strength depends on the weld penetration, and the failure originates at the weld toe on the skin side. The average transverse and axial tensile strengths reach 87.8% and 53.1% of the base materials and the fracture mechanisms of the transverse and axial tensile tests are found to be ductile and brittle fracture, respectively. The average longitudinal tensile strength reaches 90.8% of the base materials, and the average elongation is 8.4% of the original test specimens. The dimples are small and shallow, the fracture is a mixture of ductile and brittle fracture, and a tearing trace near the fusion line appears. Fatigue failure is found to originate at the weld toe on the skin side and finally crack on the skin, and the conditioned fatigue strength is 80.7 MPa. The fracture at the weld toe is a mixture of ductile and brittle fracture, and the skin panel fracture appears brittle fracture feature.