The backlight unit may include a plurality of optical assemblies, which each include a light emitting module having a substrate, a plurality of light emitting devices on a top surface of the substrate, and a connector provided on a bottom surface of the substrate and electrically connected to a power supply unit. The optical assembly may also include a light guide plate including a first part through which the light is received and a second part to output the light, which is laterally received from the first part, through a top surface thereof. A first side cover may be provided over the light emitting module and the first part of the light guide plate. A second side cover may be formed under the light emitting module and the light guide plate, the second side cover having a plurality of connector holes. The connector may be provided in one of the connector holes.