The present invention is to provide a package bag having a metal layer, wherein the metal layer is formed with a first groove and a second groove, and the second groove has a first side extending to one edge of the metal layer and a second side away from said edge and communicating vertically with a central section of a first side of the first groove. The second side of the second groove is shorter than the first side of the first groove, such that the portions of the metal layer adjacent to the first side of the first groove form two first impedance-matching portions respectively, and the two corresponding portions of the metal layer adjacent to the first groove form two second impedance-matching portions respectively. Thus, due to the impedance-matching portions, a slot antenna can be formed on the metal layer for coupling with a communication device attached thereto.