Provided are a thin film transistor and method of fabricating the same, in which an amorphous silicon layer is formed on a substrate, a capping layer containing a metal catalyst having a different concentration according to its thickness is formed on the amorphous silicon layer, the capping layer is patterned to form a capping layer pattern, and the amorphous silicon layer is crystallized, such that the density and position of seeds formed at an interface between the amorphous silicon layer and the capping layer pattern is controlled, thereby improving the size and uniformity of grains, and in which polycrystalline silicon of desired size and uniformity is selectively formed at a desired position by one crystallization process, resulting in a thin film transistor having excellent and desired properties.