In this study, the impact of laser quenching on 45 steel (V-shaped notch) is researched and the effect of laser power on the fracture toughness is investigated. The specimens surface and fracture morphology are examined by optical microscope and scanning electronic microscope (SEM). Dimple characteristics are observed on the fracture surface of original specimens. As comparison, there are brittle fracture characteristics in the crack initiation zone of laser hardened specimens. Our results indicate that the fracture toughness of laser hardened specimen is reduced. Moreover, the surface fracture toughness decreases with increasing of the laser power.