The invention discloses a backlight unit. The backlight unit includes a light source for generating light and a light guide plate for guiding the light in an upward direction, a top surface of the light guide plate includes a plurality of first and second lens patterns which extend in a first direction, the first lens pattern and the second lens pattern are alternately arranged in a second direction crossing the first direction, and a width the first lens pattern in the second direction increases gradually from a first width to a second width greater than the first width and then decreases gradually from the second width to the first width repeatedly along the first direction.