Phase equilibria in the Al-rich region of the Al–Mn–Ni alloy system were studied at 1000, 950, 850, 750, 700, 645 and 620°C. Three ternary thermodynamically stable intermetallics, the φ-phase (Al5Co2-type, hP26, P63/mmc; a=0.76632(16), c=0.78296(15)nm), the κ-phase (κ-Al14.4Cr3.4Nil.1-type, hP227, P63/m; a=1.7625(10), c=1.2516(10)nm), and the O-phase (O-Al77Cr14Pd9-type, Pmmn, oP650,: a=2.3316(16), b=1.2424(15), c=3.2648(14)nm), as well as three ternary metastable phases, the decagonal D3-phase with periodicity about 1.25nm, the Al9(Mn,Ni)2-phase (Al9Co2-type, P1121/a, mP22; a=0.8585(16), b=0.6269(9), c=0.6205(11)nm, β=95.34(10)°) and the O1-phase (base-centered orthorhombic, a≈23.8, b≈12.4, c≈32.2nm) were revealed. Their physicochemical behaviour in the Al–Mn–Ni alloy system was studied.