An approach for wideband radar cross section (RCS) reduction of a microstrip antenna is proposed based on 2.5-dimension (2.5D) miniaturized frequency selective surface (FSS). The reference microstrip antenna works at 2.5GHz, and the resonant frequency of FSS is the same. At the resonant frequency, the designed FSS shows a band-stop characteristic in order to preserve the radiation performance. Compared with the reference antenna, results show that a wideband RCS reduction from 1 to 13GHz (except the operation band of antenna) is obtained by replacing the solid metal ground with the 2.5D miniaturized FSS, and a remarkable RCS reduction for TE polarization and TM polarization at 2.1GHz is 10.07dB and 15.68 dB, respectively. 2016 IEEE.