A display device includes a lens with an adjustable refractive index. The display device includes a display panel including a plurality of pixels, a backlight unit positioned at a back side of the display panel to emit light of a first color and light of a second color to the display panel at different times, the first color and the second color being different from each other; and a lens unit positioned at a front side of the display panel to form at least one lens in a 3D mode. The lens unit includes a plurality of electrodes for adjusting a refractive index of the lens, and a signal applied to the electrodes when the backlight unit emits the light of the first color is different from a signal applied to the electrodes when the backlight unit emits the light of the second color.