Abstract: An icosahedral phase in a rapidly solidified Al₆₆ Mn₁₄ CU₂₀ alloy is identified by means of analytical electron microscope (AEM). The selected area diffraction patterns from the phase show a fivefold symmetry of a quasicrystalline structure. The energy dispersive analysis of X-ray (EDAX) for the phase indicates that it is a ternary of composition Al₁₁Mn₃Cu₆. After being heated, the ⅠPhase in Al-Mn-Cu alloy willtransform to T Phase.