A backlight unit for a liquid crystal display device includes a reflection plate, first and second light guide plates over the reflection plate, the second light guide plate disposed between the first light guide plate and the reflection plate, wherein the first light guide plate includes first and second sections alternating with each other, and the second light guide plate includes third and fourth sections alternating with each other, the first and third sections having patterns at rear surfaces, the second and fourth sections excluding patterns, wherein the first section corresponds to the fourth section, and the second section corresponds to the third section, first and second light-emitting diode (LED) assemblies at opposite sides of the first and second light guide plates, each of the first and second LED assemblies including LEDs arranged in first and second lines, and a plurality of optical sheets over the first light guide plate, wherein the LEDs of the first lines of the first and second LED assemblies face opposite side surfaces of the first light guide plate, and the LEDs of the second lines of the first and second LED assemblies face opposite side surfaces of the second light guide plate.