A thin film transistor substrate for applying a horizontal electric field and a fabricating method thereof for simplifying a process are disclosed. In a liquid crystal display device according to the present invention, a gate line on a substrate; a data line crossing the gate line having a gate insulating film there between to define a pixel area; a thin film transistor including a gate electrode, a source electrode, a drain electrode and a semiconductor layer to define a channel between the source electrode and the drain electrode; a common line on the substrate; a common electrode in the pixel area; and a pixel electrode in the pixel area to form a horizontal electrode field with the common electrode, wherein the data line, the source electrode and the drain electrode have an opaque conductive pattern and a transparent conductive pattern, the pixel electrode is formed by an extension of the transparent conductive pattern of the drain electrode, and a protective film borders with the transparent conductive pattern and in the remaining area thereof.