The effect of different Sn contents on microstructure evolution, tensile behavior, and wear properties of AZ91 alloys by rheocasting was studied. The results show that the presence of Sn changes the solid solubility of Al in Mg matrix and effectively refines the microstructure of alloy matrix. The average grain size is refined from 105.0 μm to 42.1 μm after addition of 0.8wt% Sn. The heterogeneous precipitate nuclei are formed by the intermetallics with high melting point, which effectively refines the magnesium matrix during the rheo-solidification. These dispersed second phases suppress the formation of dendrites, further improving the mechanical properties. With increasing the Sn content, the wear rate of alloys is obviously decreased and the abrasive wear disappears gradually. The rheocast AZ91 alloy with addition of 3.0wt% Sn has the highest tensile strength and the best wear resistance.