An active device array includes a plurality of scan lines, a plurality of data lines, a plurality of pixel structures, a first testing circuit, a second testing circuit, a third testing circuit and a fourth testing circuit. Each of the pixel structures is connected to one of the scan lines and one of the data lines. The first testing circuit is electrically connected to the odd scan lines; the second testing circuit is electrically connected to the (4n+1)th scan lines wherein n is zero or a positive integer; the third testing circuit is electrically connected to the even scan lines; the fourth testing circuit is electrically connected to the (4n+2)th scan lines.