This work studied the phases in the Al corner of the Al-Mn-Be phase diagram in the as-cast state and heat-treated conditions. Metallographic investigations, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were used for identifying the phases. The Be contents in the identified phases were precisely determined using Auger electron spectroscopy. The results indicated that Al₆Mn does not dissolve Be, whilst λ-Al₄Mn dissolves up to 7 at.% Be. The average composition of the T phase, which is normally designated as Al₁₅Mn₃Be₂, was 72 at.% Al, 19 at.% Mn, and 9 at.% Be. The phase with the nominal composition Be₄AlMn contained more Al than Mn. The atomic ratio Al:Mn was between 1.3:1 and 2:1. The hexagonal Be-rich phase did not dissolve any Al and Mn. The icosahedral quasicrystalline (IQC) phase contained up to 45 at.% Be. The compositions of T phase, λ-Al₄Mn, IQC, and Be₄AlMn may vary, however, the ratio (Al + Be):Mn remained constant, and was close either to four or six indicating substitution of Al atoms with Be atoms in these phases.