Effects of Nd content on the microstructure and mechanical properties of Mg-5.0Y-xNd-0.6Zr（x=0,1.0,1.8,2.6,3.4,4.2，mass fraction/%）alloy casts are investigated by optical microscopy(OM), scanning electron microscopy(SEM), differential scanning calorimetry(DSC), X-ray diffractometry(XRD) and tensile tests. The results reveal that increasing Nd content can refine the average grain size of alloys from 33.5 μm to 19.2 μm, reduce the number of Y atom in α-Mg and Mg24Y5 grain dispersed in the matrix, and increase β phase with the distribution of discontinuous network in crystal boundary. With the increase of Nd content, the tensile strength keeps rising first and subsequently falling, and the yield strength has a sharp increase at first and then gradually becomes constant, with the maximum values of 214.5 MPa and 102.8 MPa, respectively. The elongation and section shrinkage linearly decrease from 16.4% and 23.8% to 4.9% and 2.7% with the increase of Nd content. The mechanism of grain size refinement of Mg-5.0Y-xNd-0.6Zr alloys can be explained by Nd and Y enrichment in the forefront of solid-liquid interface during solidification process which enhances the supercooling of the solute rich zone and inhibits the crystal grain growth.