The microstructure, phase composition, and mechanical properties during heat treatment and rolling of the novel Al-5.0Cu-3.2Er-0.9Mn-0.3Zr alloy were evaluated. A new quaternary (Al,Cu,Mn,Er) phase with possible composition Al₂₅Cu₄Mn₂Er was found in the as-cast alloy. Al₂₀Cu₂Mn₃ and Al₃(Zr,Er) phases were nucleated during homogenization, and θ″(Al₂Cu) precipitates were nucleated during aging. The metastable disc shaped θ″(Al₂Cu) precipitates with a thickness of 5 nm and diameter of 100-200 nm were nucleated mostly on the Al₃(Zr,Er) phase precipitates with a diameter of 35 nm. The hardness Vickers (HV) peak was found after the annealing of a rolled alloy at 150 °C due to strengthening by θ″(A₂Cu) precipitates, which have a larger effect in materials hardness than do the softening processes. The novel Al-Cu-Er-Mn-Zr alloy has a yield strength (YS) of 320-332 MPa, an ultimate tensile strength (UTS) of 360-370 MPa, and an El. of 3.2-4.0% in the annealed alloy after rolling condition.