Effects of different RE （rare earth） additions on the microstructure and mechanical properties of AZ61 alloys during hot deformation were investigated.With 1%～4% mischmetal addition,β-Mg17Al12 phase in as-cast microstructure of AZ61 magnesium alloy is greatly decreased,and grain size is obviously refined,and acicular,rod-like or irregular block Al4Ce phase or compound phase of Al4Ce and Al3Nd which is distributed into grain boundary or grain can be observed,meanwhile,irregular block α-Al8Mn5 phase can be observed in the experimental alloys too.During hot deformation process,Al4Ce phase or compound phase of Al4Ce and Al3Nd can refine microstructure of the alloy by inhibiting growth of grain or sub-grain,which slightly improves the mechanical properties of the alloy,however,compared with those of AZ61 matrix alloy,mechanical properties of the AZ61 alloy with RE addition are sharply deteriorated as a result of coarse RE phase dissevering grain boundary and binding force in grains.Fracture mechanism of as-cast AZ61+xRE alloy is characterized by brittle crack,and that of as-extruded AZ61 alloy is characterized by ductility-brittle crack,and that of as-extruded AZ61+xRE alloy is characterized by cleavage crack.