The intergranular corrosion behavior, exfoliation corrosion behavior, stress corrosion behavior and microstructures of 2099 Al-Li alloy in different aging conditions were investigated by OM, TEM and slow strain rate tensile testing. The results show that the corrosion resistance of the alloy is improved with aging time. In the under-aged condition, the remained AlCuFeMn phases at grain boundaries result in low corrosion resistance of the under-aged alloy. In the peak-aged condition, many T1 phases precipitate in the matrix, promoting the incensement of corrosion resistance of the alloy. In the over-aged condition, a great number of T1 phases still remain the morphology as that in the peak-aged alloy, and the coarse precipitates distribute along the grain boundaries with large space inducing the further growth of corrosion resistance of the alloy.