An axle of railway wheel sets and a corresponding method for the ultrasound inspection are described. A blind hole, coaxial to the axle and sized to accommodate an ultrasonic probe, is obtained in each end of the axle. Main holes are intended to accommodate the probe holder containing a plurality of ultrasonic transducers for the inspection of the axle from the inside of the hole. The main advantage is to facilitate the propagation of the ultrasounds without being subjected to the interference caused by the geometric discontinuities normally present at the ends of the axles thereby minimizing false positives in the readings of the echoes.