The microstructures and mechanical properties of Mg–2.0Zn–1.0Mn (ZM21) alloys with certain amount of Ce and Nd additions were investigated, and the influence mechanism of Ce and Nd on the microstructures and mechanical properties of extruded alloys was discussed. The results indicated that the addition of Nd and Ce can refine the grains in ZM21 alloy, for which the distribution density of second phase particle played a major role to hinder the growth of dynamic recrystallization (DRX) grain in alloys by adding a content of 0.4 wt.% Ce and Nd. The average grain size of ZM21 alloy with the additions of 0.4 wt.% Nd and Ce reached 6 ± 3 μm and 13 ± 2 μm, respectively. Adding Ce and Nd to ZM21 alloy, the changes of mechanical properties were mainly attributed to a reduction in basal texture intensity, refinement grain size as well as the dispersion density and distribution position of fine second phase particles. Furthermore, by addition of Ce and Nd to ZM21 alloy, the non-basal plane slip system could be activated which decreased the basal texture intensity