A display panel and a light source device used therein are provided. The display panel includes a light-guide thin-film circuit substrate, a light source and a polarizing layer. The light-guide thin-film circuit substrate has a light entrance end and a light exit top surface, and the light source is disposed corresponding to the light entrance end. The polarizing layer is disposed on the light-guide thin-film circuit substrate and parallels the light exit top surface of the light-guide thin-film circuit substrate. The light produced by the light source enters the circuit substrate through the light entrance end, guided and transmitted through the circuit substrate, and then leaves the circuit substrate through the light exit top surface and enters the polarizing layer. The light after passing through the polarizing layer is turned into a polarized light having flat light source effect as a backlight source for the system. A polarizer may even be disposed between the light source and the light entrance end, so the light is turned into polarized light before entering the circuit substrate.