A new tunable band-notched ultra wideband planar monopole antenna is presented. The proposed antenna consists of a wideband planar monopole antenna, band-notched resonating stubs, and varactor diodes. To generate the tunable band-notched characteristic, we applied a short-circuited quarter-wavelength stub with a varactor diode to the wideband planar monopole antenna. We show the mechanism for notch characteristic using surface current distribution. This new approach is suitable for designing wideband antenna with narrow band interferer rejection characteristic. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2829-2832, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24744