In this study, failure analysis of the axle of a 4-wheeled vehicle was carried out. The part broke during daily use, causing an accident. The axle is made of 4340 alloy steel material. In order to understand the cause of the damage, visual inspection, and then, fatigue analysis was performed. As a result of visual inspection, signs of fatigue damage were observed. The analysis was advanced based on this initial information. As a result, it was concluded that the damage was due to the sudden load caused by fatigue.