A backlight unit is discussed, which includes a frame including a bottom and a sidewall extending from the bottom; at least one substrate located on the frame, and a plurality of light sources mount on the at least one substrate; and a reflecting sheet located on the at least one substrate, wherein the reflecting sheet includes: a first sheet part located on the bottom, the first sheet part including a plurality of holes corresponding to the plurality of the light sources; a second sheet part extended from the first sheet; and a third sheet part extended from the second sheet part and located on the sidewall; wherein the second sheet part comprises a plurality of dot areas positioned sequentially in a direction from the first sheet part to the third sheet part and the plurality of dot areas include a first dot area and a second dot area, the first dot area including a plurality of dots having the same size and the second dot area including a plurality of dots having the same size, and wherein a size of the plurality of dots in the first dot area is different from a size of the plurality of dots in the second dot area.