Abstract: With pure magnesium and Mg-30Ce master alloy as raw materials, the Mg-Ce alloy with 1wt% Ce was prepared by casting, and treated by solution at 420 ℃ for 8 h and aging at 200 ℃ for 20 h. The change of rare earth phase distribution in the alloy in different states was studied. The results show that the rare earth phases of the as-cast, solution-treated and aging-treated alloy were all Mg₁₂Ce. The distribution of rare earth precipitation phases in the as-cast alloy was uneven, which was dominated by boundary precipitation and supplemented by in-grain precipitation, and the size and morphology of the precipitation phase were quite different. After solution treatment, most of the precipitated rare earth phase was soluted in the magnesium matrix, but there were still a certain number of rare earth phases at grain boundaries and in part of grains. After the aging treatment, the rare earth phase uniformly dispersed in grains, and the amount of precipitation at grain boundaries was smaller. Compared with the as-cast sample, the precipitated phase after aging was smaller in size and distributed more uniformly.