The effects of yttrium addition on microstructure and mechanical properties of extruded Mg-Zn-Y-Zr magnesium alloys were investigated by using optical microscope(OM), X-ray diffraction(XRD) and scanning electron microscope(SEM) et al. It was shown that the addition of yttrium resulted in the formation of the new phase, Mg3Zn3Y2, which distributed both on the grain boundaries and inside the grains. With the increasing of Y content, the amount of Mg3Zn3Y2 phase increases and the size becomes uniform. Grain refinement was found especially with 5.92%Y addition and a certain amount of coarse grains were formatted in the alloy with 3.95% Y addition, which led to the decline of the mechanical properties. The yield strength of the Mg-Zn-Y-Zr alloys was improved with the addition of Y, but the tensile strength was not changed obviously.