A backlight unit includes a bottom cover, a light source, a middle mold, a diffusion plate and an optical sheet. The bottom cover defines a bottom portion and a sidewall portion which is protruded from the bottom portion. The light source is accommodated in the bottom cover. The middle mold is supported by the bottom cover and defines a horizontal supporting portion and a distance maintaining portion extending from a first end of the horizontal supporting portion in a direction perpendicular to the bottom portion. The diffusion plate overlaps the horizontal supporting portion. The optical sheet overlaps the distance maintaining portion and is spaced apart from the diffusion plate.