The effect of minor scandium addition on the microstructures and mechanical properties of Al-Zn-Mg-Cu-Zr alloys has been studied. Three alloys were produced by casting and then extruded to rods. Tensile properties of these alloys in different condition were tested. The relationship between mechanical properties and microstructures of the alloys was discussed in detial. The results showed that the tensile strength of Al-9.0Zn-2.5Mg-1.2Cu-0.15Zr-0.12Sc and Al-9.0Zn-2.5Mg-1.2Cu- 0.15Zr-0.20Sc in solution and T6 reaches 763.7MPa and 774.6MPa, respectively, while the elongation remains 5.7% and 8.3%, respectively.