Abstract: Effects of MIG welding superposition on microstructure and property of 6A01-T5 FSW joint was researched in this work. The results indicated that the MIG/FSW joints formed well without porosity defects near the superposition. The microstructure of the FSW weld nugget and heat affected zone became coarse and which near the superposition was changed obviously. The hardness value of the superposition was reduced significantly, especially for FSW thermo-mechanically affected zone and heat affected zone. The tensile strengths of the FSW joint, MIG superposition on the FSW weld center, MIG superposition on the FSW advancing side thermo-mechanically affected zone, and MIG superposition on the FSW retreating side thermo-mechanically affected zone were 219.8 MPa, 188.0 MPa, 195.4 MPa and 191.4 MPa, respectively. MIG superposition reduced the FSW joint tensile strength, and the fracture appearance of all joints belonged to ductile fracture. The median fatigue strengths of above the FSW joint and three joints with MIG weld reinforcement were 76.7 MPa, 65.0 MPa, 67.5 MPa and 65.0 MPa respectively. The MIG superposition was also reduced the fatigue properties of the FSW joints.