An active device array substrate including a substrate, a pixel array, pads, first switching devices, and second switching devices is provided. The pixel array is disposed on a display region of the substrate. The pads, the first and the second switching devices are disposed on a peripheral circuit region of the substrate. The pads and the pixel array are electrically connected. The first and the second switching devices are at the outside of the pads. Each first switching device is electrically connected to one of the pads and has a source, a drain, and a gate electrically connected to the source and the pad. Each second switching device is electrically connected to two adjacent first switching devices and has a gate, a source, and a drain. The source and the drain are electrically connected to the drain and the source of the adjacent first switching device, respectively.