Fractal antenna has more advantages compared with conventional antenna in size reduction and multi-frequency performance because of its special space filling capability. Fractal is used in the radar cross section (RCS) reduction of antenna in this paper. Compared with normal rectangular microstrip patch antenna, the radiating edges of microstrip patch antenna are designed in the shape of Koch fractal, while two Koch fractal shape slots are cut in the antenna. The RCS of the fractal antenna is effectively reduced both in band and out of band compared with the rectangular patch antenna, while the radiation performance is almost maintained. Based on the design, antenna prototypes were fabricated and tested, which validate the theory.Based on the low RCS antenna element designed, the RCS of array antenna is also researched. By comparing the standard rectangular patch array with fractal patch array in the situation of equal phase center and equal distance between elements, we find that, the miniaturization of fractal reduces the mutual coupling of elements,improves the array radiation character and reduces the structural mode scattering field of array antenna.