The tensile and fatigue strength of cast Mg-xNd-0.2Zn-0.45Zr alloys (x = 0, 1, 2, 3 wt%) in both solution-treated (T4) and solution + 200 A degrees C peak-aged (T6-PA) conditions were investigated in the present study. The results indicate that Neodymium (Nd) is an effective element to improve both the tensile and fatigue properties of cast Mg-0.2Zn-Zr alloys. The strengthening effect depends on its content in a way of power function (sigma A = sigma(0) + K C (Nd) (n) ), where the power exponent n is about 0.52-0.54 for yield strength (YS) and 0.59-0.61 for fatigue strength. The yield strengthening effect of Nd element in the form of precipitates (T6-PA) is about three times of that as solution atoms (T4), while the fatigue strengthening effect of Nd element in the form of precipitates is only about 50 % higher than that as solution atoms. The improved strength (both YS and ultimate tensile strength) can lead to the same amount improvement of the fatigue strength in T4-treated alloys, while only can cause less than half improvement of the fatigue strength in T6-PA-treated alloys.