Disclosed herein are a fiber-reinforced plastic composition containing a thermoplastic resin, a reactive rubber (reactor-made thermoplastic poly olefin, RTPO), and a glass fiber; and a fiber-reinforced composite prepared from the fiber-reinforced plastic composition. Furthermore, provided is a method for preparing a fiber-reinforced composite, the method comprising the steps of: preparing a thermoplastic resin composition by feeding a thermoplastic resin and a reactive rubber into a first extruder, followed by melting and kneading; preparing a fiber-reinforced plastic composition by feeding the prepared thermoplastic resin composition and a fiber into a second extruder, followed by kneading; and molding the prepared fiber-reinforced plastic composition to prepare a fiber-reinforced composite.