A very low profile monopole ultra-wideband (UWB) antenna with band rejection characteristics is presented. The antenna is designed to reject the frequency bands of WiMAX and WLAN while the size of the antenna is miniaturized significantly. The overall size after extensive optimization of the antenna's dimensions is 12×18 mm2. A half-wavelength slot in the radiator of the antenna is used to introduce a frequency band-notch at the WiMAX frequency band. However, the WLAN frequency band is notched using two symmetrical open-ended quarter-wavelength slots in the ground plane. The proposed antenna is simulated, fabricated, and its performance is measured experimentally. The simulation and measurement results demonstrate the suitability of the proposed antenna to work properly in the UWB systems.