A backlight unit has a frame, at least one optical film, and at least one light source accommodated in the frame. The frame has a top wall, a bottom wall opposite to the top wall, two opposite side walls, and at least one protuberance integrated on the top wall. The at least one optical film includes at least one through-hole with respect to the at least one protuberance. The at least one protuberance drills through the at least one through-hole for hanging the at least one optical film on the frame.