Friction stir welding (FSW) is a recently developed solid state welding method, and now being used increasingly for joining aluminium alloys. However, the fatigue behaviour of FSW joints with relatively complicated microstructure is still unclear. In this study, fatigue behaviour of FSW joints of 6061-T6 aluminium alloy was investigated. The 6061-T6 plates were joined with welding speeds of 100 and 200 mm/min and the rotation speeds of tool of 1200 and 1800 rpm. Fatigue tests were conducted at stress ratio
= −1 under axial loading.