The thermal conductivity and the tensile properties of Mg-3Zn-xSn (x=0.5, 1.5, 2.5, 3.5, wt%) alloys were studied. The thermal conductivities of the alloys with different contents of Sn were measured at 25 °C and 100 °C. The results clearly show that the thermal conductivity decreases with the increase of Sn content, and increases with the rise of temperature. Meanwhile, the ultimate tensile strength and the elongation of the alloys increase with the increase of Sn content. With the increase of Sn content the thermal conductivity of the alloys decreases, while the mechanical properties increase.