This study demonstrates a local peening method using a tool with small tip radius. Frist, the effect of material strength on the improvement by the method was investigated, which showed the fatigue strength of the peened joint was improved to the level of the base metal with tensile strength grades of 440 MPa and 980 MPa. Second, the effect of the peening pattern was investigated, which showed the width of the peening pattern affected the crack initiation site. Finally, the technique improved the fatigue life of a closed-section lower suspension control arm more than three times by enhancing the fatigue strength of the weld toe.