An optical sheet, a backlight unit including the optical sheet, and a liquid crystal display including the backlight unit may be provided. The optical sheet may include a reflective polarizing film, a base film on one surface of the reflective polarizing film, and a plurality of projections on the base film. The base film may include a first surface and a second surface opposite the first surface. A first thickness T1 is a distance between the first surface and the second surface and a second thickness T2 is a distance between the first surface and the second surface. The first and second thickness T1 and T2 satisfy the following equation: 0.1 μm≦|T1−T2|≦10 μm.