The effect of different microstructures on the fatigue behaviour of a medium carbon vanadium microalloyed steel has been studied. Specimens were subjected to a controlled closed die forging followed by cooling in sand, air or oil, respectively. The hardness and fatigue properties of the microalloyed steel are determined and compared with those of ferrite-pearlite and martensite microstructures obtained by cooling with different mediums after forging. Relatively fine ferrite and pearlite increase the fatigue strength of the steel, while the martensite structure reduces the fatigue strength. Characteristics of fatigue fracture surface morphology are summarized and related to fatigue crack initiation and propagation mechanisms in the forged medium carbon microalloyed steel. The cooling rate has a remarkable effect on the microstructure, hardness, and fatigue behaviour at room temperature.