Friction　stir　weld　fatigue　test　was　performed　and　the　microstructure　of　the　welded　joint　was　analyzed　on　aluminum　2219-T6.　The　surface　morphology,　micro-hardness　and　grain　structure　of　the　welded　joint　were　observed.　The　fracture　surface　of　the　welded　joint　was　observed　after　the　fatigue　test.　According　to　the　observations,　there　were　more　dynamic　recrystallizations　in　the　nugget　zone　and　the　grain　size　became　smaller　in　this　zone.　The　grains　in　the　thermo-mechanical　affected　zone　deformed　obviously　and　there　were　more　substructures　in　the　heat　affected　zone.　The　hardness　values　were　lower　in　the　thermo-mechanical　affected　zone　and　nugget　zone.　The　hardness　values　distribution　shape　was　W　in　the　upper　surface　of　the　joint　and　probably　V　in　the　bottom　surface　of　the　joint.　The　fatigue　fractures　happened　mostly　in　the　nugget　zone.　There　were　lots　of　inner-hole　defects　in　nugget　zone　on　the　fracture　surface　by　scan　observation.　These　defects　could　affect　the　properties　of　the　welded　joint.　©　(2014)　Trans　Tech　Publications,　Switzerland.