Abstract: In order to determine the properties of refill friction stir spot welded (RFSSW) Al-Mg alloys joints,tests on tensile/shear strength,cross-tension strength,microstructure and fatigue properties of refill friction stir spot welded joints were conducted with 2 mm-thickness 5A06 aluminum alloy as research subject,and microstructure model of RFSSW joint was established as well. Experimental results indicated that the microstructure of the joints could be divided into nugget zone,heat affected zone,thermo-mechanically affected zone and base material, respectively. When the rotational speed was 2 000 rpm,the tensile/shear strength was able to reach 8 194 N,and the highest cross-tension strength was 3565N. SEM and OM analysis showed that fatigue cracks initiated from weld edge on the joining surface of the upper and lower plates,and defects including ring groove, cavity,aluminum clad in this area,as well as stress concentration were the main causes for fatigue damage.