Abstract: Smooth and notched specimens were prepared from LZ50 steel axle to test the rotating bending fatigue property according to the new standard of AAR M-101-2009 and observe the fracture morphology. The results show that rotating bending fatigue cracks initiated from the smooth sample surface, while the cracks in notched specimen initiated from the notch edge, and the cracking shape was multi-source. The fracture surfaces of the two kinds of samples were perpendicular to axial direction. After the tensile strength of the axle increased by 5%, the rotating bending fatigue property of smooth sample increased significantly; the medium fatigue strength of notched sample was 18% less than that of smooth sample, but the notch sensitivity coefficient of rotating bending fatigue limit remained at the same level with the overseas carbon steel axle.