An active device array substrate includes a substrate, a pixel array, a peripheral circuit, and a number of marks. The substrate has an active area and a peripheral circuit area that is connected to the active area. The pixel array is disposed on the active area of the substrate. The peripheral circuit is disposed on the peripheral circuit area of the substrate. Besides, the peripheral circuit includes a number of driver bonding pads, a number of fan-out lines, and a number of connecting lines. The fan-out lines are electrically connected to the pixel array. Each of the connecting lines connects one of the driver bonding pads and one of the fan-out lines. Additionally, the connecting lines are arranged in different pitches. Each of the marks is disposed between two adjacent connecting lines.