Connecting rod is an important component, where the connecting rod is used as a link between the piston and the crankshaft to transmit the force from the piston to the crankshaft. In this research, the connecting rod is buckling so that several tests would be carried out to analyze the mechanism and causes of the failure. The tests carried out were visual observation, chemical composition testing, metallographic testing, hardness testing and FEM simulations. The results of visual observations showed that the failure of the connecting rod was buckling at the bottom of the small end. The chemical composition test shows that the material used is AISI 4130 steel which is a low alloy steel. The microstructure that is formed is the ferrite and pearlite phases on the failed part and martensite on the part far from the failed part, because the oil in the engine runs out so there is no lubricant and coolant so that the temperature rises and causes the connecting rod decrease in hardness value, the hardness test results show if the material has an average hardness of 500 HV on the part far from failure and 350 HV on the part that fails, this proves that the main cause of failure of the connecting rod is a decrease in the hardness value. The FEM simulation results show that the total deformation due to the engine motion mechanism is in the part that has failed, this also supports why the connecting rod failure.