Mg-Zn-Sn alloys with different w（Zn）/w（Sn）mass ratios were prepared in permanent mould

and microstructure and mechanical properties of the as-cast alloys were investigated.The results reveal that when the total amount of Zn and Sn is constant[w（Zn）+w（Sn）=8%]

with the w（Zn）/w（Sn）mass ratios increase

the grain boundary of the alloys becomes coarser and the number of second phase or eutectic phase on the grain boundary are increased.The mechanical properties of the alloy are increased firstly and then decreased with the increase of w（Zn）/w（Sn）mass ratios.The alloy with w（Zn）/w（Sn）mass ratios of 5/3 has the desirable strength

where the compressive strength reaches 296 MPa

and the alloy with w（Zn）/w（Sn）ratio of 3/5 has the highest compression ratio of 21.5%.The mechanism was described of addition elements Zn

Sn and w（Zn）/w（Sn）mass ratio affecting strength and toughness of Mg-Zn-Sn alloys.