The microstructural evolution and phase transformations of a high-alloyed Al–Zn–Mg–Cu alloy(Al–8.59Zn–2.00Mg–2.44 Cu, wt%) during homogenization were investigated. The results show that the as-cast microstructure mainly contains dendritic α(Al), non-equilibrium eutectics(α(Al) + Mg(Zn,Al,Cu)2), and the θ(Al2Cu) phase. Neither the T(Al2Mg3Zn3) phase nor the S(Al2Cu Mg) phase was found in the as-cast alloy. The calculated phase components according to the Scheil model are in agreement with experimental results. During homogenization at 460°C, all of the θ phase and most of the Mg(Zn,Al,Cu)2 phase were dissolved, whereas a portion of the Mg(Zn,Al,Cu)2 phase was transformed into the S phase. The type and amount of residual phases remaining after homogenization at 460°C for 168 h and by a two-step homogenization process conducted at 460°C for 24 h and 475°C for 24 h(460°C/24 h + 475°C/24 h) are in good accord with the calculated phase diagrams. It is concluded that the Al–8.59Zn–2.00Mg–2.44 Cu alloy can be homogenized adequately under the 460°C/24 h + 475°C/24 h treatment. The microstructural evolution and phase transformations of a high-alloyed Al-Zn-Mg-Cu alloy (Al-8.59Zn-2.00Mg-2.44Cu, wt%) during homogenization were investigated. Neither the T (Al2Mg3Zn3) phase nor the S (Al2Cu Mg) phase, but also the non-equilibrium eutectics (α (Al) + Mg (Zn, Al, Cu) 2) During homogenization at 460 ° C, all of the θ phase and most of the Mg (Zn, Al, Cu) 2 was found in the as-cast alloy phase were dissolved, whereas a portion of the Mg (Zn, Al, Cu) 2 phase was transformed into the S phase. The type and amount of residual phases remaining after homogenization at 460 ° C for 168 h and by a two-step homogenization process conducted at 460 ° C for 24 h and 475 ° C for 24 h (460 ° C / 24 h + 475 ° C / 24 h) are in good accord with the calculated phase diagrams. It is said that the Al-8.59Zn-2.00Mg-2.44 Cu alloy can be homogenized adequately under the 460 ° C / 24 h + 475 ° C / 24 h treatment.