Abstract: The joints of friction stir welding of Al-Zn-Mg-Sc-Zr alloy were investigated, and the mechanical properties and microstructures of the joint were analysed.The results show that the distribution of micro-hardness in the cross-section presents a trend of high-low-high-low-high, the maximal hardness appears in the region of the weld nugget and the lowest hardness in head-affected zone(HAZ), and the welding coefficient reaches 0.90.The weld nugget has a dynamic recrystallized, fine isometric crystal structure with the size of 1-2 μm, and the precipitation phases in the base metal are melted and broken up to small round particles;the thermo-mechanically affected zone has a highly curved structure, and the precipitation phases transform to club-shaped;the size of grains in HAZ is larger than that in the base metal.The tensile samples of welding joint break in the HAZ.