The effects of shot diameter on the bending fatigue strength test for shot-peened spring steel (JIS-SU-P9A) were investigated. The bending fatigue tests were conducted on the specimens shot peened with shot diameters of 0.2 and 0.7 mm at a stress ratio of R=0. The results of the bending fatigue tests showed that as the shot diameter decreased, the fatigue strength limit increased. It was also confirmed that there was a correlation between the residual stresses, Vickers hardness and the fatigue strength. Furthermore, the fatigue limits of the specimen were successfully predicted by using the prediction equation based on the parameter model.