The effect of Zn on the microstructure, mechanical properties and corrosion properties in Hank＇s solute on of as-cast Mg-Mn alloy was studied. The results indicate that the addition of Zn element can significantly refine the grain size of cast Mg-Mn alloy. When Zn content is increased up to 3% （mass fraction）, the grain size of the cast alloy decreases from 700-900 gm to 50-80 Ixm. Meanwhile, the mechanical properties of the alloy also increase with increasing Zn content. When Zn content is 3%, the ultimate tensile strength and the yield strength are increased by 128.8 and 42.6 MPa, respectively, while the elongation is increased twice. Addition of Zn element to Mg-Mn alloy can stabilize the passivation film, which mainly contributes to the low corrosion rate of Mn-Mn-Zn alloy. However, when the Zn content is over 3%, the passivation film becomes unstable, which results in a relatively high corrosion rate.