The present disclosure relates to a backlight unit and a liquid crystal display device having a backlight unit. The backlight unit includes a light guide plate, a light source assembly positioned adjacent to a light-incident surface among lateral surfaces of the light guide plate, and an external tape covering the entire lateral surface of the light guide plate except the light-incident surface and parts of an upper surface and a lower surface of the light guide plate. Thus, the light efficiency of the backlight unit may be increased and the manufacturing costs reduced. Further, since the light efficiency of the backlight unit is increased, the luminance and power consumption of the liquid crystal display device can be improved.