The purpose of this study is to gain a deeper understanding of the effects of rare-earth element Er on the microstructure and properties of Al-Zn-Mg-Cu alloy manufactured by laser powder bed fusion (LPBF). Compared with the as-printed Al-Zn-Mg-Cu alloy without Er addition, the as-printed Al-Zn-Mg-Cu-Er alloy with a bimodal grain structure had finer cellular structures and denser precipitation phases, which significantly improved the alloy's mechanical and corrosion resistance properties. The tensile strength of the as-printed Al-Zn-Mg-Cu-Er alloy was 383 MPa, which is 137 MPa higher than that of the as-printed Al-Zn-Mg-Cu alloy without Er addition. It was intended to use T6 heat treatment process to further regulate the mechanical properties of the as-printed alloy, but the formation of Si-rich hard and brittle eutectic phases with sizes of 2–5 μm in the matrix resulted in a decrease in the strength of the alloy, which is contrary to the traditional 7xxx aluminum alloys. Besides, the addition of Er element improved the alloy's corrosion resistance by decreasing the corrosion current density and raising the intergranular corrosion (IGC) resistance, and the maximum intergranular corrosion depth decreased from 174 µm to 68 µm after Er addition.