An active device array substrate including a substrate, a plurality of pixel units, a plurality of driving lines, a plurality of common lines, an electrostatic discharge (ESD) protection circuit, and a plurality of switch elements is provided. The substrate has a display region and a peripheral region adjacent to the display region. The pixel units are arranged as an array in the display region of the substrate. The driving lines are disposed in the display region and the peripheral region and are electrically connected to the pixel units. The common lines are disposed in the display region and are extended into the peripheral region. The ESD protection circuit is disposed in the peripheral region of the substrate. The switch elements are disposed in the peripheral region, wherein each of the switch elements is electrically connected between one of the common lines and the ESD protection circuit.