A backlight unit and a liquid crystal display device having the same which may facilitate control of output light through a light guide plate, improve light concentration effect, and reduce moire. The backlight unit includes light sources generating light, a light guide plate guiding light through an incidence surface opposite the light sources, emitting the light through an emission surface, and having lower patterns of a prism shape formed on the lower surface of the light guide plate opposite the emission surface by inclined surfaces and sub-inclined surfaces, and at least one optical sheet stacked on the emission surface.