Some Zn and a little Ag are added into ZM5 magnesium alloy (one of Mg-9 wt%Al-1 wt%Zn alloys in China), and the differences of the microstructures and properties between the new alloy and ZM5 is investigated. Effects of heat treatment and alloying elements (Zn and Ag) on the microstructure and tensile properties of Mg-9Al-xZn alloys, and relationships between the chemical composition, microstructure and properties are investigated. Zn ad Ag have obvious solid solution strengthening effects on Mg-9Al-xZn alloy, while Ag is detrimental to the corrosion resistance after being artificial aged. The morphology of pearlite-like secondary gamma(Mg17Al12) phase (gamma II) has close relation with the properties.