A thin film transistor and a fabrication method thereof, in which one excimer laser annealing (ELA) makes a pixel portion and a driver portion different from each other in surface roughness and grain size. The thin film transistor includes: a substrate including a pixel portion and a driver portion; a first semiconductor layer disposed in the pixel portion and having a first surface roughness; a second semiconductor layer disposed in the driver portion and having a second surface roughness smaller than the first surface roughness; a gate insulating layer formed on the substrate including the first and second semiconductor layers; a first gate electrode placed to correspond to the first semiconductor layer on the gate insulating layer; a second gate electrode placed to correspond to the second semiconductor layer on the gate insulating layer; an interlayer insulating layer formed on the substrate including the first and second gate electrodes; first source and drain electrodes formed on the interlayer insulating layer and electrically connected with the first semiconductor layer; and second source and drain electrodes formed on the interlayer insulating layer and electrically connected with the second semiconductor layer.