The Mg-12Gd-2Y-0.5Sm-0.5Sb-0.5Zr (wt.%) alloy was prepared by casting technology. The microstructure of alloy was then investigated after T6 heat treatment. The results show that at 523K, the alloy has shown the superior tensile strength (i.e. 345.5 MPa). When experimental alloy was stretched with temperature increasing from 293K to 523K, the increases of deformation strengthening and critical crack propagation stress caused the anomalous temperature dependence of tensile strength.