Al or Zn content of AZ31 alloy was reduced and small amounts of Sn were added to improve the formability of alloys. And the recystallization behaviors and mechanical properties of Sn added alloys were investigated. In all the investigated alloys, of which Al content was less than 3%, virtually no Mg17Al12 phase was found. Nor any Sn-containing phase was observed in either AZ21 or AM30 base alloys up to 0.75%Sn. The elongation of alloys at both room temperature and 300oC was significantly improved by the Sn additions possibly owing to increased uniformity of grain size (size difference between fine and coarse grains). Hindered recrystallization and reduced growth rate of recrystallized grains by the Sn additions are postulated to be the main reason for the enhanced grain size uniformity.