This paper has developed a multiband single-layer frequency selective surface (FSS) designed by using the optimization technique (genetic algorithm). The characteristics of the designed FSS are superior to those of the Fractal FSS in the close separation between two reflection bands. As a typical example, we design the FSS for passing L and S bands and reflecting Ku and Ka bands. Finally, the agreement between the calculated and measured transmission response for the designed FSS proves the validity of the present method.