A backlight module and liquid crystal display device are provided. The backlight module comprises a plastic frame, a reflection sheet, a light guide plate, a light source element, a hole glue and a heat dissipating element. The plastic frame comprises a first frame and a second frame disposed opposite each other. The heat dissipating element is disposed on the light source element, extending along an outer side surface of the first frame to a bottom portion of the reflection sheet, and is bonded to the corresponding hole glue on the second frame.