A backlight unit according to an exemplary embodiment of the present disclosure includes: a bottom chassis; a light source disposed on the bottom chassis; a reflective sheet disposed on the bottom chassis; at least one optical sheet disposed above the light source and the reflective sheet; and a supporter fixed to the bottom chassis and supporting the optical sheet. The supporter includes a locking portion fastened to the bottom chassis and a supporting portion extending from the locking portion, and the locking portion is positioned lower than the reflective sheet.