Two Mg-Nd-Pr alloys were prepared adopting different cooling methods, and the microstructural characteristics and phase structure of both alloys were examined by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results show that the crystalline grain size is decreased greatly under the condition of melt-spin, the supersaturated α-Mg solid solution is developed, and the mechanical properties of Mg-Nd-Pr alloy are increased remarkably. The alloying elements will precipitate along the grain boundaries in a state of slow cooling owing to lower solubility for Nd, Pr in α-Mg phase at room temperature. The phase composition of such alloy includes α-Mg, Mg41Nd5 and Mg12Pr. Mg41Nd5 and Mg12Pr are distributed in the grain boundaries. At the same time, many twins within the grains are observed.