A thin film transistor (TFT), a method of fabricating the same, and an organic light emitting diode (OLED) display device having the TFT, the TFT includes a substrate, a protection layer disposed on the substrate, a buffer layer disposed on the protection layer, a semiconductor layer disposed on the buffer layer, a gate electrode disposed on the semiconductor layer, a gate insulating layer to electrically insulate the semiconductor layer from the gate electrode, and source and drain electrodes electrically insulated from the gate electrode and connected to the semiconductor layer. The protection layer is formed of an amine-containing clay. The OLED includes the TFT, an insulating layer disposed on the TFT, a first electrode connected to the drain electrode of the TFT, an organic layer disposed on the first electrode, and a second electrode disposed on the organic layer.