The effects of Sn addition on the microstructure and tensile properties of as-cast AZ80 alloy were investigated by the means of OM, XRD, SEM and tensile property test. The microstructure of as-cast AZ80-xSn (x=1, 3, 5, wt.% ) alloys appears typical equiaxed dendrites morphology, which consists of a-Mg primary, divorced eutectic (Mg+Mg₁₇Al₁₂), laminar Mg₁₇Al₁₂, divorced eutectic Mg₂Sn. The addition of Sn elecment effectively suppressed the laminar Mg₁₇Al₁₂ phase precipitating duringSsolidification. When the Sn content was 5 wt.%, the laminar Mg₁₇Al₁₂ phase nearly disappeared. The grain size reduced when the Sn content less than 3 wt.%. Moreover, The alloy was strengthened significantly by Sn content and the AZ80-3Sn alloy had the superior mechanical property.