Abstract: Mg–Sn–Y alloys with different Sn contents (wt%) were assessed as anode candidates for Mg-air batteries. The relationship between microstructure (including the second phase, grain size, and texture) and discharge properties of the Mg–Sn–Y alloys was examined using microstructure observation, electrochemical measurements, and galvanostatic discharge tests. The Mg–0.7Sn–1.4Y alloy had a high steady discharge voltage of 1.5225 V and a high anodic efficiency of 46.6% at 2.5 mA·cm⁻². These good properties were related to its microstructure: small grain size of 3.8 μm, uniform distribution of small second phase particles of 0.6 μm, and a high content (vol%) of (\begindocument 11\overline20 \enddocument)/( 10\overline10 ) orientated grains. The scanning Kelvin probe force microscopy (SKPFM) indicated that the Sn₃Y₅ and MgSnY phases were effective cathodes causing micro-galvanic corrosion which promoted the dissolution of Mg matrix during the discharge process.