Provided are a backlight and a liquid crystal display device including the same. The backlight unit includes a light source assembly which emits light; a light guide plate which receives at a light incident surface thereof light from the light source assembly; and a bottom chassis having a bottom unit on which the light guide plate is disposed. The bottom unit of the bottom chassis has a first bottom portion which is arranged in the vicinity of the light incident surface and has a first recess, a second bottom portion which is bent diagonally to the cross sectional surface and has a second recess, and a third bottom portion which is bent at the second bottom portion in the direction parallel to the first bottom portion and disposed higher than the first bottom portion. A light absorbing member is disposed in the first and second recesses.