In this work, the effects of rare element yttrium (Y) on the microstructure and mechanical properties of the as-cast Zn-25Al-5Mg-2.5Si alloy at room and elevated temperature (100°C and 180°C) have been investigated. The alloys were prepared by conventional melting and casting routs with different Y contents (0 wt.%,0.1 wt.%,0.4 wt.%,0.8 wt.%,1.2 wt.% and1.5 wt.%). The results showed that the addition of Y element led to the formation of Al3Y phase and Y2Zn17 phase in the microstructure and the mechanical properties of the alloys rose at first and then dropped with the Y content increasing. When Y content was 0.4 wt.%, the optimization of microstructure and properties especially the tensile strength at high temperature was obtained. The tensile strength of the alloy at 180°C could be increased by 26.4%.