Abstract: The effects of Zn contents on microstructure, mechanical properties and damping properties of cast Mg-Zn-Zr alloys were studied, and damping mechanism for the tested alloys was discussed.The results show that the compressive strength of Mg-Zn-Zr alloys increased and damping properties decresed with the increase of Zn content. When Zn content was 3.18wt%, the alloy showed relatively good mechanical properties and damping properties. The damping mechanism for the tested alloys was not affected by Zn contents and could be explained by G-L theory, and was anelastic internal friction at low strain amplitude, and static hysteresis internal friction at high stain amplitude.