The present invention provides a display device with feedback brightness sensing, suitable for using in a PDA, that comprises a LCD panel at an outside of which is installed a first photo-sensor for sensing a light brightness variation of its environment. A corresponding sensing signal is delivered to a first converter to be converted to a first digital reference signal that is delivered to a microprocessor for determining a brightness increase or decrease of the display panel. Via a light-guiding element and a second photo-sensor installed within the display panel, the light brightness from the display panel is sensed and converted to a second digital reference signal that is compared with the first digital reference signal to determine whether the display brightness is at an optimal value. An automatic brightness adjustment of the display device is thereby achieved to reduce power consumption and protect the user's eyes.