In this paper, a novel frequency selective surface (FSS) is designed for reduction of radar cross section (RCS) level in the reflectarray antenna. A 9x9 variable size FSS structure is constructed on double opposite side geometry. The reduction of RCS performance is compared with ground plane backed and designed FSS backed reflectarray antenna. The simulation results demonstrate that the FSS backed reflectarray antenna can achieve the reduction of RCS level in-band and out-of-band. Also gain and radiation performance of FSS backed reflectarray antenna is nearly same with ground plane backed reflectarray antenna.