A portable communication device includes an appearance, a substrate and a switchable resonant antenna. The substrate is disposed in the appearance, and the substrate has a ground plane. The switchable resonant antenna comprises a first connection portion, a switching unit, a first metal element and a second metal element, where the first connection portion is electrically coupled between the ground plane and the switching unit, the switching unit is configured to electrically couple the first connection portion to the first metal element or the second metal element according to a control signal generated corresponding to a detecting result, in order to generate a first resonant mode.