The effects of repeated tempering process on the microstructure and machinability of AISI 52100 steel in terms of cutting force, cylindricity and surface roughness were investigated in the present study. Specimens were annealed at 850 degrees C for 60 minutes. The specimens were then rapidly quenched in oil. Quenched samples were tempered at various tempering temperatures (175, 225, 300 and 400 degrees C) and numbers of passes (1 and 2) in a tempering furnace. Machining tests were carried out at various cutting speeds (30, 45, 60 and 70 m x min(-1)), various feed rates (0.15, 0.20 and 0.25 mm x rev(-1)) and at a constant depth of cut at 0,4 mm after repeated tempering. The experimental results show that repeated tempering temperature and number of passes significantly affect microstructure and machinability of AISI 52100 steel. The hardness of the AISI 52100 steel decreases with increasing number of temperings and temperature. The lowest cutting force was obtained at the highest cutting speed and the lowest feed rates. The machinability of AISI 52100 can be optimized by repeated tempering heat treatment.