High-cycle rotary bending fatigue tests were conducted on a supercarburized low-alloy steel. Special attention was paid on how the eutectoid carbide contained in the material affects the fatigue process. The metallographic and fractographic observations of the fatigue process, revealed that although debonding at the matrix/carbide interface occurs at the initial stage of the fatigue process, final failure was induced by the growth of a crack initiated at the weak site of retained austenite grains. At the fatigue limit, the growth of the weak-site-initiated crack was blocked by the surrounding carbide particles.