Back light unit of flat panel display

A BLU(Back Light Unit) of a flat panel display is provided to improve the light efficiency as removing each one of prism sheets and diffusion sheets, thereby achieving luminance characteristics more than the two sheets and accordingly reducing costs and improving productivity. A backlight unit of a flat panel display comprises a light source, a installed in its side, a reflective sheet(1) for reflecting light of the light source, a crossing-type light guide panel(20), a prism sheet(40) installed on the crossing-type light guide panel, and a diffusion sheet(6) installed on the prism sheet. The crossing-type light guide panel is installed on the reflective sheet. On an upper surface of the light guide panel, a continuous pattern of an "X" shape is formed to form prison protrusions(24) of a mountain shape. Between the prism protrusions, a dot(21) is formed.