Abstract: Based on the S-N curves,the comparision of fatigue performance for 5A06 aluminimum alloy friction stir welding(FSW) and MIG(metal inert-gas) welded joints were conducted,and the effects of welding defects during FSW on the fatigue properties of FSW joints were discussed.It was shown that the fatigue strength of FSW joints was obvious higher than that of MIG joints because of the influence of different weld geometrical shape etc.,and the kissing-bond defects at the root of FSW joints was the important factor to reduce the fatigue strength of FSW joints,and the rotating ridge produced by the friction stir tool shoulder on the weld surface of FSW would have an apparent decrease on the fatigue life.