An LED backlight unit comprising: a lower cover; a plurality of boards provided on the lower cover, each of the boards being disposed horizontally to the bottom surface of the lower cover; a plurality of light guide plates provided on the lower cover, the plurality of light guide plates being arranged in parallel with each other; a plurality of LED packages mounted onto the plurality of boards and supplying light through a side of one adjacent light guide plate of the plurality of light guide plates; and characterized in that the plurality of light guide plates is provided above the plurality of boards, each of said plurality of light guide plates partially overlapping at least one respective board of said plurality of boards; the lower cover has a plurality of first through holes; the plurality of boards have a plurality of second through holes facing the first through holes of the lower cover, respectively; and the LED backlight unit further comprises a plurality of fixation units engaged with the second through holes of the board and the first through holes of the lower cover so that one edge of each of the plurality of light guide plates is pressed against the lower cover; wherein the fixation units are engaged with the board and the lower cover between one light guide plate and another light guide plate disposed adjacent to each other when inserted into the first through holes and the second through holes and fixing simultaneously the light guide plates disposed adjacent to each other; and wherein each of the fixation units comprises a head which partially covers one upper edge of each of the respective adjacent light guide plates, and a body extending from the head and inserted into a respective through hole from the plurality of second through holes of said plurality of boards. a lower cover; a plurality of boards provided on the lower cover, each of the boards being disposed horizontally to the bottom surface of the lower cover; a plurality of light guide plates provided on the lower cover, the plurality of light guide plates being arranged in parallel with each other; a plurality of LED packages mounted onto the plurality of boards and supplying light through a side of one adjacent light guide plate of the plurality of light guide plates; and characterized in that the plurality of light guide plates is provided above the plurality of boards, each of said plurality of light guide plates partially overlapping at least one respective board of said plurality of boards; the lower cover has a plurality of first through holes; the plurality of boards have a plurality of second through holes facing the first through holes of the lower cover, respectively; and the LED backlight unit further comprises a plurality of fixation units engaged with the second through holes of the board and the first through holes of the lower cover so that one edge of each of the plurality of light guide plates is pressed against the lower cover; wherein the fixation units are engaged with the board and the lower cover between one light guide plate and another light guide plate disposed adjacent to each other when inserted into the first through holes and the second through holes and fixing simultaneously the light guide plates disposed adjacent to each other; and wherein each of the fixation units comprises a head which partially covers one upper edge of each of the respective adjacent light guide plates, and a body extending from the head and inserted into a respective through hole from the plurality of second through holes of said plurality of boards.