In this study, a novel single layer band stop Frequency Selective Surface (FSS) for gain enhancement of Ultra-Wide Band (UWB) antenna is presented. The proposed FSS unit cell consists of a conventional square loop (CSL), a ring and cross dipole elements and printed on a single side of 15mm x 15mm dielectric substrate. The -10dB frequency band relies on 3.02GHz and 11.79GHz and fractional bandwidth is % 128. Also, effects of the unit cell parameters over the transmission performances are investigated and conclusions are presented. In order to showgain enhancement performance, the FSS with the designed high gain UWB antenna were simulated by CST MWS. The antenna with FSS has a maximum gain of 14dB. The FSS shows a linear reflection phase variation within the operation range and can be good candidate for enhancing the printed antennas gain.