Mg-25Sn-xZn alloys were prepared by mechanical alloying and hot-press sintering methods using Mg powders, Sn powders and Zn powders as raw materials. The effects of the Zn content on microstructures and mechanical properties of the Mg-25Sn alloys were studied. The results show that Zn didn"t participate with the alloying reaction in the mechanical alloy process of Mg-25Sn-xZn system, but the introduction of Zn reduced the size of Mg+Mg₂Sn mixture. The Zn in the sintered Mg-25Sn-xZn was completely transformed into MgZn₂ phase except the solution. And with the increase of the Zn content, the size of MgZn₂ phase gradually increased. MgZn₂ phase was preferentially distributed along Mg grain boundary and around Mg₂Sn particle phase. When the Zn addition is 6wt%, the Mg-25Sn alloy exhibited excellent mechanical properties, hardness, yield strength, fracture strength and strain are 1.60GPa, 388MPa, 497MPa and 7.5% respectively.