A mobile communication device is provided. The mobile communication device includes a system circuit board with a surface, a ground plane having a monopole slot on the surface, a microstrip feedline, and a metal element, wherein the ground plane has a longer edge and a shorter edge. The monopole slot has a first operating band and a second operating band. The microstrip feedline is located on the system circuit board, wherein one end of the microstrip feedline passes over the monopole slot, and the other end of the microstrip feedline is connected to a signal source. The metal element is electrically connected to the shorter edge of the ground plane, and is substantially perpendicular to the ground plane. A distance between the open end of the monopole slot and the shorter edge of the ground plane where the metal element is connected is shorter than 0.05 wavelength of the lowest operating frequency of the first operating band.