A novel planar octagonal-shaped antenna with reduced radar cross section (RCS) for ultra-wideband (UWB) applications is designed and demonstrated experimentally. The proposed antenna is modified using the geometrical shaping method in order to get the RCS reduction. This method is based on the subtraction of metal areas which have the minimum current distributions on the surface of printed antenna. Both of the reference and modified octagonal-shaped antennas are operating at 2.5-18 GHz frequency range with %151 fractional bandwidths. The full-wave electromagnetic simulations and laboratory measurements are performed to characterize their RCSs as a function of frequency, radiation patterns and scattering characteristics. The radiation performance of modified antenna is stable and consistent with the reference antenna. Also the results show that the designed UWB antenna has lower RCS compared to the reference antenna. About 10 dBsm RCS reduction is obtained in the whole operation bandwidth. The designed antenna has very large RCS reduction up to 25 dBsm, especially in the low frequency range.