The present invention relates to an ultra-wideband (UWB) antenna, which comprises: a rectangular aperture portion, formed from a ground plane of a printed circuit board and having an aperture; and a co-plane feeding structure, having a horizontal portion and a vertical portion, wherein the vertical portion is perpendicular to the horizontal portion, and the vertical portion is disposed in the aperture and connected with an external terminal. The ultra-wideband (UWB) antenna of the present invention can receive the wireless signal with 3.1˜10.6 GHz band, and have a very compact area (13 mm×23 mm) and is easy to be mass produced. Furthermore, a parasitism element can be added into the co-plane feeding structure, so as to reject the in-band interferences from the existing systems like 5˜6 GHz signals of wireless LAN.