Abstract: The effect of Mn alloying on hydrogen embrittlement (HE) in Al-0.1Cu-(0.5, 0.9 and 1.4) Mn (mass%) alloys was investigated. Optical microscopy and X-ray diffraction revealed that all three Mn-alloyed samples exhibited a fully face-centered cubic structure with similar grain sizes. After hydrogen charging and tensile testing, the sample containing0.9 mass% Mn showed the poorest resistance to HE. Plastic strain distribution observed by digital image correlation indicated more severe strain localization during tensile deformation in the hydrogen-charged 0.9Mn alloy. Furthermore, a higher number of precipitates was observed in the 0.9Mn alloy, which accelerated HE. Fractography by scanning electron microscopy revealed secondary cracks in the hydrogen-charged 0.9Mn alloy, further confirming its inferior resistance to HE. Thus, Mn alloying can effectively control HE in Al-Cu-Fe-Mn alloys, but the Mn content should avoid0.9 mass% to prevent severe HE.