An active matrix substrate including a substrate, a plurality of pixel units, a plurality of driving lines, an electron static discharge (ESD) protection circuit and a floating line is provided. The substrate has an active region and a peripheral region connected with the active region. The pixel units are arranged in a matrix in the active region. The driving lines electrically connected to the pixels are disposed in the active region and the peripheral region. The ESD protection circuit and the floating line are disposed in the peripheral region of the substrate. The ESD protection circuit is electrically connected to the driving lines. The ESD protection circuit includes an outer short ring (OSR) and an inner short ring (ISR) disposed between the pixel units and the OSR. The floating line is located beside the outer driving line.