Solid solution effects on the hardness and flow stress in Mg–Sn binary alloys with Sn content between 0.18% and 2.18% at temperatures ranging from ambient to 623K were investigated in this study. At room temperature, the hardness increases with the Sn content as H v0.5 =28.3+6.88c, the 0.2% proof strength (corrected for grain size strengthening effect) and c n follow a linear relationship, where c is the solute atom fraction and n=1/2 or 2/3. The results suggest that the strengthening of basal planes controls the solid solution strengthening in polycrystals of Mg–Sn binary alloys. However, the c n power-law is not applicable in the temperature range from 423K to 623K, which is proposed to be ascribed to the competition between solid solution strengthening and softening effect.