A dual band antenna with a corrugated feed horn comprises a waveguide and a feed horn assembly. The feed horn assembly comprises at least two portions. Two portions each have at least a cylindrical ring and a groove, in which the groove is between two cylindrical rings. By means of adjusting a depth and width of the grooves and a walls width and number of loops of the cylindrical rings of two portions causes each portion responds to different frequency band electromagnetic signal separately and thereby can be adapted to receive radio signals in at least two frequency bands electromagnetic signals. Therefore, this single antenna can be adapted to receive radio signals in two frequency bands. The antenna can effectively reduce manufacturing cost and save space.