An organic light emitting display (OLED), which includes a display unit and a controlling unit, is provided. The display unit includes an organic light emission layer and a transparent thin film transistor (TFT) to drive the organic light emission layer, and the display unit emits light into two opposite surfaces (upper and lower surfaces). The controlling unit includes an electro-optical layer that is capable of being switched from one state to another state by applying voltage to the layer. The controlling unit controls transmission of light emitted from the display unit. Therefore the flat panel display of the present invention is capable of displaying an image in one surface or in two surfaces. The selection of surface of image display can be manually or automatically controlled by a user. The controlling unit can includes a liquid crystal device, an electrophoretic device, or an electrochromic device.