A rod stiffener may include a rod molded by a glass fiber reinforced thermoplastic resin, and brackets connected to both ends of the rod, in which properties of a core part forming a center of the rod and an outer part surrounding the core part are formed to be different from each other, and the properties of the core part and the outer part are differentiated by a mixing amount of glass fiber and polypropylene resin including the glass fiber reinforced thermoplastic resin.