Abstract: Supersaturated Al-Zn-Mg-Cu-Mn alloy powder was made using the spray and high energy ball milling method, and XRD was used to investigate the decomposition process of the supersaturated alloy. The results showed that the balanced phase precipitated from the supersaturated alloy was η phase (MgZn₂) when the decomposition temperature was below 350℃, and no balance or metastable phases containing manganese were detected by the XRD method. When the decomposition temperature was 350℃ for a long time, or above 350℃, there were two phases precipitated from the supersaturated alloy. One was the balanced η phase(MgZn₂), and the other was Al₆Mn, which was directly precipitated from the alloy, but not transformed from any metastable phase of manganese.