A backlight unit that minimizes damage to an optical sheet due to external impacts, and a liquid crystal display employing the backlight unit are disclosed. The backlight unit comprises a light source unit comprising a plurality of light sources; a bottom cover that receives the light source unit and comprises a first protrusion; support sides fastened to both opened shorter sides of the bottom cover to support the light source unit and comprising a second protrusion; and an optical sheet unit disposed on the light source unit and comprising a first long hole in which the first protrusion is inserted and a second long hole in which the second protrusion is inserted, wherein the first and second long holes have a dumbbell shape in which the diameter of a curved portion is larger than the width of a linear portion through which the first and second protrusions pass.