A transparent display device for enhancing optical transmissivity in a transparent mode, is discussed. The transparent display device may include a liquid crystal panel; a light source disposed at one side of a lower portion of the liquid crystal panel to emit light; a first polarizing plate for polarizing the light emitted from the light source; a light guide plate disposed at a lower portion of the liquid crystal panel to totally reflect the light polarized to an axis by the first polarizing plate to a lateral surface thereof and supply to the liquid crystal panel, and transmit natural light entered from a lower direction therethrough; and a second polarizing plate disposed at an upper portion of the liquid crystal panel to control the amount of polarized light passing through the liquid crystal panel.