A fabricating method of an array substrate for a liquid crystal display device including forming a polycrystalline silicon film on a substrate having a display region and a peripheral region, the polycrystalline silicon film having grains of square shape, forming a first active layer in the display region and a second active layer in the peripheral region by etching the polycrystalline silicon film, forming a first gate electrode over the first active layer, a second gate electrode over the second active layer and a gate line connected to the first gate electrode, and forming first source and drain electrodes connected to the first active layer, second source and drain electrodes connected to the second active layer and data line connected to the first source electrode. Further, the second gate electrode overlaps the first active layer to form a first channel region, and the first channel region is formed inside one of the grains.