This study describes an investigation of the effect of peening on the fatigue limit of rolled steel containing a crack at the weld toe. 3-point bending specimens with a weld zone were prepared for fatigue test. An artificial semi-circular slit was made into the weld toe, and subsequently the weld toe was peened by needle-peening. Using those specimens, bending fatigue tests were carried out. The following results were obtained. (1) The fatigue limits of specimens containing a slit improved considerably by peening. (2) The fracture occurred from outside the slit. Moreover, the specimens recovered to fatigue limits up to that of non-slit specimens. (3) A slit of 0.4- 1.2 mm in depth was rendered harmless by the peening.