Abstract: To improve the mechanical properties of Al-Zn-Mg-Cu alloy,0.15wt%Y was added to the tested alloy,and homogenizing,solution and aging treatment were carried out.Effect of minor Y addition on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy was studied by means of optical microscopy,X-ray diffraction and tensile testing.The results indicate that when the gross of minor Y addition to Al-Zn-Mg-Cu alloy was 0.15wt%,the size of grains in as-cast and solution states was refined evidently.The tensile strength of the alloy containing Y increased 4.7%,the yield strength increased 5.5%.However,as the residual eutectic compourds in the microstructure after homogenizing increased with the addition of minor Y,the elongation decreased 4.9%.