Creep tests of Mg-5%Zn-2%Al (-2%Y) (mass fraction) alloy were carried out at 175℃ under the load of 50MPa,on the cast and solution condition,respectively.Relationship between the creep behavior and microstructure was studied by the optical microscopy,SEM and TEM.The result shows that the primary creep strain is relative to the thermo-stability and the quantity of intermetallic compounds in grain boundary area.During the secondary creep period,the minimum creep rate of solution-treated specimens is substantially decreased as a result of dynamic MgZn2 precipitation.