The disclosure relates to the backlight unit for preventing the optical sheet from cracking and the liquid crystal display using the backlight unit. The backlight unit comprises a light having a plurality of light sources; a bottom cover housing the light and having a first protrusion; a support side engaging to both open ends of the bottom cover to support the light and having a second protrusion; an optical sheet disposing on the light and including a first hook having a first elliptical hole for inserting the first protrusion and a second hook having a second elliptical hole for inserting the second protrusion; and a first slit between an edge of the first hook and the first elliptical hole within the first hook, and a second slit between an edge of the second hook and the second elliptical hole within the second hook.