Abstract: Microstructure evolution and mechanical proprieties of friction stir welded 6082-T6 aluminum alloy were layered-investigated with transmission electron microscope(TEM), scanning electron microscopy(SEM), tensile test machine and Vickers hardness tester. The results showed that plastic deformation occurred in the upper layer of nugget zone which caused the increase of lattice distortion. Hence a large number of dislocations were accumulated into the substructure boundary with dynamic recovery to reduce energy. The grain at the top part of the weld was fine due to dynamic recrystallization by friction heat and shoulder crashing. The bottom of nugget zone which was mainly affected by stirring of the pin was composed of course grain because fewer heat was diffuse to the bottom and dynamic recrystallization and recovery were decreased correspondingly compared to the upper part of the weld. The rodlikeβ′ phase precipitated at both advancing and retreating side of heat affected zone. The microhardness distribution of both the top and bottom side of the joint along the direction perpendicular to the weld had a W shape. The minimum microhardness value appeaed at the advancing side. The tensile strength of the topside weld along welding direction was higher than that of the bottom side. The tensile strength was 205 MPa and 186 MPa respectively. The fracture mode of the weld was ductile fracture.