The utility model discloses a fluorescent whitening fiber, which is a filament bundle consisting of a plurality of monofilaments. The monofilaments in the filament bundle are arranged disorderly, thecross section of each monofilament is in the shape of a four-angle star with four 90-degree angles, and the surface of each monofilament is covered with a whitening layer. Specific surface area of thefiber is increased by utilizing four grooves formed on each four-angle star-shaped monofilament, thereby enabling the fiber to have softer hand feeling. A plurality of grooves are arranged on the textile fiber woven by the monofilaments with the four-angle star-shaped cross sections, and then the fluorescent whitening fiber is obvious in air ventilation and moisture conduction, fine in air permeability and strong in adiathermic property, and is dry and comfortable. The whitening layers are covered on the surfaces of the monofilaments, and therefore, the fiber has blue light visibly and then is whiter. A layer made of fluorescent powder is environment-friendly and pollution-free, does not have toxic and side-effect, and is high in color fastness. The fluorescent whitening fiber reduces environment pollution caused by latter dying, and is suitable for manufacturing white shirts, shoes, white socks, white medical clothes and the like.