The effects of shot peening on the three-point bending fatigue limit are described for LC9 aluminum alloy. Examination of the fatigue fracture surfaces revealed that the fatigue cracks were initiated under the hardened layer, depending upon the compressive residual stress (CRS) distribution. In this case, the local fatigue limit at the fatigue source is about 1.38 times of that of unstrengthened ones. An explanation is given with reference to the concept of internal fatigue limit бwi, which is regarded as the critical stress to initiate propagative fatigue microcrack in the interior of metal. and an intrinsic property of metal.