Abstract: The friction stir welding of 2.8 mm thick 1420 aluminum-lithium alloy was conducted.The mechanical property and microstructure of the joints as well as the influences of welding parameters were investigated. The results show that if the welding parameters are optimal, the tensile property and elongation of the joints can reach to 90% that of the base metal, and the higher heat input could improve the mechanical properties.SIM and microhardness analysis indicate that fracture surface was characterized by main cleavage and dimples.Compared with other area, the hardness in weld was higher, and the highest area was in the center of the weld.The maximum is the TMAZ area at the retreating sides.The microstructure behaves the 'S' characteristic.