A display device including a timing controller, a data driving circuit and a display system is provided. The timing controller outputs first pixel data according to input pixel data, wherein a color depth of the first pixel data is a first bit number or a second bit number smaller than the first bit number. The data driving circuit receives the first pixel data and a notice signal, and maps the first pixel data to generate second pixel data according to the notice signal when the color depth of the first pixel data is the second bit number, and directly takes the first pixel data as the second pixel data when the color depth of the first pixel data is the first bit number, and generates at least one driving voltage according to the second pixel data, wherein the color depth of the second pixel data is the first bit number.