A backlight assembly includes a light providing unit, an optical sheet, and a mold frame. The light providing unit generates light. The optical sheet has a main body disposed on the light providing unit and a sheet-guiding portion protruding outward from the main body. The mold frame has a frame shape to receive the light providing unit and the optical sheet and includes a sheet-guiding recess and a securing protrusion adjacent to at least one side of the sheet-guiding recess and protruding with respect to an upper surface of the optical sheet to prevent misalignment of the optical sheet. The sheet-guiding recess receives the sheet-guiding portion.