Provided is a package structure including a composite wafer, a plurality of dies, an underfill, and a plurality of dam structures. The composite wafer has a first surface and a second surface opposite to each other. The composite wafer includes a plurality of seal rings dividing the composite wafer into a plurality of packages; and a plurality of through holes respectively disposed between the seal rings and penetrating through the first and second surfaces. The dies are respectively bonded onto the packages at the first surface by a plurality of connectors. The underfill laterally encapsulates the connectors. The dam structures are disposed on the first surface of the composite wafer to separate the underfill from the through holes.