Abstract: Friction stir welding was carried out on 3 mm and 4 mm thick 6061-T6 aluminum alloy plates at high welding speeds (3 000 mm·min^-1), respectively. The effect of high rotational speed (4 000-6 000 r·min^-1) on microstructure and tensile properties of the joints was studied. The results show that the smaller the rotation speed, the easier the formation of hole defects. The higher the rotation speed was, the easier the overheated oxidation appeared. Increasing rotation speed was conducive to the recrystallization of the joint area to form a dense structure. The welding defects of welded joints of 4 mm thick aluminum alloy plates were more serious than those of welded joints of 3 mm thick aluminum alloy plates. The welding joint quality and tensile properties of 3 mm thick aluminum alloy plate at a rotation speed of 5 000 r·min^-1 were the best, and the tensile strength and elongation after fracture were 265.82 MPa and 4.58%, respectively. The welding joint quality and tensile properties of 4 mm thick aluminum alloy plate at a rotation speed of 6 000 r·min^-1 were the best, and the tensile strength and elongation after fracture were 212.14 MPa and 4.03%, respectively.