A viewing-angle adjustable liquid crystal display includes a display panel, a backlight unit, and a sidelight unit. The backlight unit is located under the sidelight unit, and the sidelight unit is disposed under the display panel. The sidelight unit includes a first sidelight source and a light-guide plate. The first sidelight source is disposed at one end of the light-guide plate. The displaying method includes providing direct light to the display panel in response to the narrow-viewing-angle-mode signal; and providing scattering light to the display panel in response to the wide-viewing-angel-mode signal.