This report deals with fatigue properties of the thin wall ductile cast iron and effect of casting surface. Fatigue tests were conducted with as-cast and surface machined test pieces made of ductile cast iron in the shape of thin plate 2mm thick. The fatigue limit of as-cast test piece was smaller than that of machined ones. Fracture origin and its size were investigated by SEM observation. Most of the fracture origins were concavity of casting surface, and others were micro shrinkages and dross. Measurement manner of concavities on the casting surface as the fracture origin was examined. Fracture origin size was also estimated by the profile of the casting surface to predict fatigue properties. The size of the fracture origins were evaluated well with the depth and the radius at the bottom of the concavity. Evaluation with the depth and the width of the concavity is overestimate, compare with the experimental results. Estimated fatigue limit by the profile of the casting surface was 259MPa, and it was agreed well with the fatigue limit of the experimental results of 252MPa. Fatigue limit can be predicted by the profiles of the casting surface.