The effects of trace Mn addition on microstructure and mechanical properties of 2297 Al-Li alloy were investigated by optical microscopy, tensile test, scanning electron microscopy(SEM), transmission electron microscopy(TEM) and scanning transmission electron microscopy(STEM), fitted with high-angle annular dark field detector(HAADF). The results show that Mn exists in the form of AlCuMn rod-like dispersed particle and Al(CuMnFe) coarse phase in 2297 alloy. In addition, the Al(CuMnFe) phases in 2297 alloy are uniformly distributed and the size of the coarse particles is smaller than that in Mn-free alloy. As a result, the tensile strength of 2297 alloy was enhanced. The study indicates that the addition of Mn has no influence on the precipitation behavior of Al3Zr. And the level of recrystallization in 2297 alloy has not been changed, though the AlCuMn rod-like dispersed phases are precipitated.