The aim of this work is to study the residual stress profile generated by conventional and ultrasonic shot peening in a 41CR4 steel steering ball joint as well as to evaluate the effect of these two mechanical surface treatments on the fatigue behaviour of this automotive part. The stress field generated by both processes has been evaluated using X-ray diffraction and incremental hole drilling methods. The results reveal that it is possible to generate a higher prestressed :layer with a smaller surface roughness by ultrasonic shot-peening than by the conventional process. Moreover, the ultrasonic shot peened parts present a higher fatigue resistance than the conventional shot peened materials. Ultrasonic treatments can thus be a serious competitor to conventional shot peening processes.