A backlight unit for a display device and a liquid crystal display device using the backlight unit suppresses light leakage to a neighboring region with a display area that is divided and driven by a DDAM (Divided Display Area Method). The backlight unit in one aspect includes a main light guide plate defined by an n number of regions for a field sequential driving, auxiliary light guide plates arranged below edges of the main light guide plate, first and second reflection plates arranged below the main light guide plate and the auxiliary light guide plate, a plurality of light source parts arranged at a predetermined interval at both sides of the auxiliary light guide plate, and a housing configured to enclose a side of the main light guide plate, the auxiliary light guide plate and side and lower portion of the light source parts.