The intergranular corrosion susceptibility of Al-Mn alloys containing Mn up to 1.22% depends on Mn content and heat treatments. Al-0.5%Fe-0.15%Si alloys containing Mn0.3% or more are susceptible to intergranular corrosion. Heating at brazing temperature near 600°C results in recrystallization and dissolution of Al6Mn or Al6(Mn, Fe) in the Al-Mn alloys. Al6Mn or Al6(Mn, Fe) compounds precipitate preferentially at grain boundaries during cooling or aging after heating at brazing temperature. Cathodic polarization of the Al-Mn alloys decreases with increase of Al6Mn or Al6(Mn, Fe) precipitation. The Al-Mn alloys in which Al6Mn or Al6(Mn, Fe) precipitates at random and ones in which Mn dissolves in the matrix are unsusceptible to intergranular corrosion. The intergranular corrosion susceptibility of Al-Mn alloys is, however, intensified by precipitation of Al6Mn or Al6(Mn, Fe) at grain boundaries.