A multi-frequency antenna includes a first antenna element, a second antenna element, a connection element, a third antenna element and a shorted element. The connection element is connected between the first antenna element and a neighborhood portion of the third antenna element. A feeding point is located in or nearby a first junction between the connection element and the first antenna element or located in the connection element. The shorted element is connected between the second antenna element and the grounding plane. The shorted element extends from a second junction between the second antenna element and the third antenna element to the grounding plane. The first conductive path that extends from the feeding point to the other end of the shorted element is substantially equal to a second conductive length that extends from the feeding point to the free end of the first antenna element.