In this study, the effect of shot peening on fatique strength of SAE 9245 steel, which is used in industry for spring production, was investigated. Shot peening process was carried out to create residual compressive stresses caused by deformation hardening at the surface and to remove decarburized layer of the surface resulted in heat treatment. The fatique specimens were heated up to 850 degreesC and held at that temperature for 20 min to transform microstructure completely to austenite and hardened by water quenching. The specimens were then tempered at 500 C to eliminate residual stresses caused by the quenching. A group of fatique specimens, only as heat-treated and other specimens shot peened by using an air high-pressure type of equipment with CS 230 shot, was tested on Wohler fatique test machine. The fatique results for unpeened and peened conditions were compared. It was seen that shot peening improved the fatique life by about 30%. (C) 2002 Elsevier Science B.V. All rights reserved.