Abstract: Welding defects can be also formed during friction stir welding under improper welding technology conditions, and the friction stir welding defects such as groove, void and kissing bond significantly influence the mechanical properties of joints. Friction stir welding process is utilized to repair these defects, and the focus is placed on the weld morphology and mechanical properties of the repaired joints. The experimental results indicated that the friction stir welding process can remove the above-mentioned welding defects, and the repaired joints have good weld morphology and excellent mechanical properties when optimum repair parameters are used. The fracture analysis showed that the repaired joints are ruptured on the retreating side of the weld in the tensile test, and the fracture surfaces are characterized by the clear plastic deformation dimples.