Provided is a circuit board, including a first substrate, a second substrate, a third substrate, a fourth substrate, multiple conductive structures, and a conductive via structure. The second substrate is disposed between the first substrate and the third substrate. The third substrate is disposed between the second substrate and the fourth substrate. The third substrate has an opening penetrating the third substrate and includes a first dielectric layer filling the opening. The conductive via structure penetrates the first substrate, the second substrate, the first dielectric layer of the third substrate, and the fourth substrate, and is electrically connected to the first substrate and the fourth substrate to define a signal path. The first substrate, the second substrate, the third substrate and the fourth substrate are electrically connected through the conductive structures to define a ground path, and the ground path surrounds the signal path.