The leaf spring is frequently applied on a vehicle such as used on the truck and it is one of the machine element suspension systems. It needs to have an excellent resistance to the fracture propagation to avoid failure that could lead to severe accidents. Fracture failure on the leaf spring is frequently experienced especially on diesel trucks, known as premature failure. Therefore, this case is needed to be studied and investigated. The purpose of this study is to investigate the cause of failure on the broken leaf spring by counting analytically the stress intensity factor (KI) occurred near the crack tip. Moreover fracture surface observation conducted by Scanning Electron Microscope (SEM) to find out whether there is or not an initial crack and crack propagation direction. This present study describes the experimental work and analytical analysis of theleaf spring used on Diesel Truck Vehicle. Hardness testing was performed using the Rockwell method. The chemical composition testing on the leaf spring material was found that the material in accordance with AISI 5150 standard. The hardness value of leaf springs tested of about 106.9 HRB. The result of analytical analysis shows that the maximum value of stress intensity factor (KI) occurred near the crack tip at the near the hole of leaf spring. In this case the value of KIis higher than thevalue of the fracture toughness (KIC) of the leaf spring material. Therefore, this result could be inferred that crack propagation happened starting from initial crack tip which is located near the hole on the leaf spring. The failure of leaf springs also caused by fatigue crack propagation due to dynamic loading during the operation marked by appearance the beach mark on the fracture surface.