A method for fabricating an active device array substrate is provided. First, a substrate having a display area and a sensing area is provided. Then, a first patterned conductor layer is formed on the display area of the substrate. A gate insulator is formed on the substrate. A patterned semiconductor layer, a second patterned conductor layer and a patterned photosensitive dielectric layer are formed on the gate insulator, wherein the second patterned conductor layer includes a source electrode, a drain electrode and a lower electrode, the patterned photosensitive dielectric layer covering the second patterned conductor layer includes an interface protection layer disposed on the source electrode and the drain electrode and a photo-sensing layer disposed on the lower electrode. A passivation layer is then formed on the substrate. After that, a third patterned conductor layer including a pixel electrode and an upper electrode is formed on the passivation layer.