A backlight unit for a liquid crystal display. The backlight unit comprises a frame, a first supporting portion, a second supporting portion, and a film. The film comprises a first constraining portion and a second constraining portion. The film is positioned on the frame by the first and the second supporting portion passing through the first and the second constraining portion, respectively. When the frame is disposed in a first position, the first supporting portion partially contacts an inner wall of the first constraining portion for positioning the film. When the frame is disposed in a second position, the second supporting portion partially contacts an inner wall of the second constraining portion for positioning the film. An LCD utilizing the backlight unit is also disclosed.