Abstract: Forging stock of bearing steel used for railway locomotive was pretreated by water quenching. The forging stock and water quenching pretreated steel were subjected to austenitizing and isothermal quenching. The effect of water quenching pretreatment on the microstructure and mechanical properties of the bearing steel was studied. The results show that the microstructure of forged bearing steel was composed of pearlite and ferrite, and after water quenching pretreatment was composed of martensite and a little ferrite. After austenitizing and isothermal quenching, slender bainite slat bundles and massive martensite/austenite (M/A) islands appeared in both forging stock and water quenching pretreated steel. The bainite slat bundles in the water quenching pretreated steel were smaller, and M/A islands were more in amount and smaller in size. The tensile strength and yield strength of the water quenching pretreated steel after austenitizing and isothermal quenching were 8.68% and 17.07% higher than those of the forging stock, respectively, and the impact energy was also higher than that of the forging stock. But the elongation after fracture of the two was similar.