Friction stir welded 5 mm thick, Al-Li alloy rolled sheet, metallurgical, hardness and tensile strength measurements were performed. The results demonstrate that there exist three distinct zones in the FSW joint: the weld nugget zone (WNZ), and the thermal-mechanically affected zone (TMAZ), and the heat-affected zone (HAZ). The microstructures in WNZ take on scale shape. Under the thermal cycle, the microstructures in HAZ occur recovery and generate the bar-shape recovery structure. The microstructures in TMAZ consist of the equiaxed grains, and the grain size of the microstructures at the retreating side is bigger than that at the advancing side. The tensile test results confirm that the highest tensile strength of Al-Li FSW joints welded with a cylinder-shape and non-thread pin is 296MPa(under the welding speed υ =40mm/min), and the highest elongation percentage is 8.6%( under the welding speed υ =80mm/min).The hardness measurements show that the weld is softened, and the softened scope of both the advancing and the retreating sides are almost the same. But the soften degree of the material at the retreating side is higher than that at the retreating side.