Abstract: Online heat treatment is an effective process for enhancing the strength, hardness, and wear resistance of steel rails. Taking U75V rail steel as research objects, and the tensile properties, impact toughness, hardness distribution, and microstructure of hot-rolled and online heat-treated rail specimens were comparatively analyzed. The results show that after online heat treatment, the tensile strength, elongation after fracture, tread Brinell hardness, and cross-sectional Rockwell hardness of the rail specimens are all superior to those of the hot-rolled rails. In particular, the impact toughness increases by nearly 2 times. Microstructural analysis reveals that the rails in both states consist of pearlite with a small amount of proeutectoid ferrite, but the pearlite interlamellar spacing, cementite thickness, ferrite thickness, and pearlite colony size of the heat-treated rails are all smaller than those of the hot-rolled rails.