Provided are a method of fabricating a multilayered thin film transistor using a plastic substrate and an active matrix display device including the thin film transistor fabricated by the method. The method includes: preparing a substrate formed of plastic; forming a buffer insulating layer on the plastic substrate; forming a silicon layer on the buffer insulating layer; patterning the silicon layer to form an active layer; forming a gate insulating layer on the active layer; stacking a plurality of gate metal layers on the gate insulating layer; patterning the plurality of gate metal layers; and etching a corner region of the lowest gate metal layer formed on the gate insulating layer of the patterned gate metal layers. Accordingly, a gate metal is formed which includes a multilayered gate metal layer and has an etched corner region, thereby reducing an electric field of the corner to reduce a leakage current of the TFT.