The microstructure and tensile properties of 5A90 aluminum-lithium alloy rolled plate after heat treatment were studied with optical microscope, scanning electron microscope and transmission electron microscope. The results showed that the microstructure of the as-rolled plate presented anisotropy. Equiaxed grain appeared in the rolling plane. The microstructure in the longitudinal section and cross section presented a rolling streamline. There were a small number of recrystallized grains within the alloy. With the ageing heat treatment at 130 ℃ after the solid solution of 460 ℃/20 min, the hardness of the alloy increased continuously with ageing time until 20 hour peak-ageing, then the hardness dropped slowly. The main precipitate strengthening phase of 5A90 alloy was δ'(Al3Li) phase, and there was a good coherent relationship between δ′ phase and the matrix at peak-ageing. The ultimate tensile strength, yield strength and elongation were 512 MPa, 437 MPa and 7.5%, respectively. The main fracture manner of 5A90 aluminum-lithium alloy was dimple fracture, delamination cracking and cracking along the sub-boundaries. Tensile fracture surfaces showed the mixed characteristics of ductile fracture and brittle fracture.