A novel planar ultra-wideband (UWB) antenna with triple-notched bands using triple-mode stub loaded resonator (SLR) is presented in this paper. The basic UWB antenna consists of a circular- shaped radiating element, a 50 Ω microstrip feed line, and a partially truncated ground plane. Then, the resonance properties of the SLR are studied. Results reveal that the multiple-mode property of the SLR can be utilized in the UWB antenna design to achieve triple band-notched performance. To validate the design concept, a novel planar UWB monopole antenna with three notched bands respectively around the WiMAX band, WLAN band, and X-band satellite communication band is designed and fabricated. The results indicate that the proposed planar antenna not only retains an ultrawide bandwidth, but also owns triple band-rejections capability. The UWB antenna demonstrates omnidirectional radiation patterns across nearly whole operating bandwidth that is suitable for UWB communications.