Effects of different Nd contents on high cycle fatigue of die cast magnesium alloy AZ91D have been examined at the condition of stress ratio of 0.1.The results indicate that with increasing in Nd contents,the grain size in microstructure of the alloy is refined gradually,and the size and amounts of β-Mg 17Al 12 phase are decreased and dispersively distributed.With Nd contents increase,the tensile strength,elongation and condition fatigue strength of die cast AZ91D+xNd alloy can be improved,where the maximum tensile strength of 207 MPa,elongation of 6.8% and condition fatigue strength of 70 MPa can be observed with 1.0% Nd addition.SEM analysis shows that the alloy containing 1%Nd exhibits the maximum fatigue propagation regions.There exists rip edge and dimple in rupture of three different Nd content alloys,showing quasi-cleavage and toughness fracture.