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Rotating bending fatigue tests were carried out on the SP treated ADI (ADI-SP) specimens, and the fatigue properties were investigated from the viewpoints of fatigue strength, crack initiation behavior and residual stress change. The following points are main conclusions from this study. 1. There were the hardened layer and the compressive residual stress region of about 400 micrometer from the surface induced by shot-peening treatment in the ADI specimens 2. The S-N diagram of the non-treated ADI (ADI-AC) specimens showed clear horizontal part in the regime of 10(exp6) to 10(exp8) cycles, and the diagram got down again over 10(exp8) cycles. But, the S-N diagram of the ADI-SP specimens did not exist such a clear horizontal part before 10(exp8) cycles. 3. The improvement of fatigue strength for the ADI-SP was confirmed before the regime of the 10(exp7) cycles. However, the S-N diagrams of the ADI-SP and the ADI-AC specimens crossed at near 10(exp8) cycles, and the fatigue strength of the ADI-SP specimens became lower than that of the ADI-AC specimens. 4. All of fracture in the ADI-AC showed typical surface fracture type, and the fracture origins were casting defects, a group of spheroidal graphites or large size graphites near surface. However, all of fracture in the ADI-SP specimens showed internal fracture type origination from the internal casting defects. 5. The distributions of the initial residual stresses were scarcely changed during fatigue loading, and the crack origins sites were at a depth where the residual stress was tensile in nature in the ADI-SP specimens.