Abstract: The fatigue and mechanical properties of 16Mn steel welded joint by rolled prestrain have been determined with the rotating bending specimens. The fractograph and dislocation morphology were observed by means of SEM and TEM. The experimental results indicate that the fatigue limit of the material by rolled prestrain was apparently reduced although its strength and hardness were increased. The fatigue fractograph of the material with microprestain showed entire embrittle feature; and the dislocations were mostly multiplicated and displayed cell substructure. It is considered that special structure of the dislocation and damage accumulation induced by rolled were main factors to make the fatigue strength of the welded joint reduced after rolled prestrain.