Organic light emitting display device

An organic light emitting display device is presented which prevents water from penetrating through an outermost side of a display panel, thereby enhancing reliability of first thin film transistors (TFTs). The organic light emitting display device includes a base substrate, a first buffer layer disposed on the base substrate, a TFT disposed on the first buffer layer in a display area, a second TFT disposed on the first buffer layer in a non-display area, an organic light emitting diode (OLED) disposed on the first TFT, and an encapsulation layer disposed on the OLED, the second TFT, and the first buffer layer. The first buffer layer and the encapsulation layer each include the same material, for example, silicon oxynitride (SiON).