Disclosed are an oxide semiconductor thin film transistor and a method of fabricating the same. An oxide semiconductor thin film transistor according to an embodiment of the present disclosure includes a substrate; a first gate electrode formed on the substrate; a gate insulator formed on the first gate electrode; an oxide semiconductor layer formed on the gate insulator; source and drain electrodes formed by depositing carbon nanotubes (CNTs) and a metal electrode on the formed the oxide semiconductor layer and patterning the deposited CNTs and metal electrode such that the source electrode and the drain electrode are spaced apart from each other; and a passivation layer formed on the formed source and drain electrodes, wherein the source and drain electrodes serve to prevent diffusion of a metal of the metal electrode into the formed oxide semiconductor layer, due to the CNTs of the source and drain electrodes.