A backlight unit for use in a liquid crystal display comprises a light guiding plate comprising a light exiting surface, a light reflective surface, and a light incident surface, a light source unit comprising a substrate and a light source disposed on the substrate, wherein the light source unit is disposed to face the light incident surface of the light guiding plate, and a reflecting sheet comprising a first portion facing the light reflective surface of the light guiding plate, a second portion facing the light exiting surface of the light guiding plate, and a third portion connecting the first and the second portions, wherein the third portion comprises light source exposing parts.