A new photocatalyst, namely single-crystalline Bi 5 O 7 NO 3 nanofibers, was prepared by a facile hydrothermal method in the presence of Triton X-100 and ammonia. Bi 5 O 7 NO 3 possessing a crystalline sheet morphology could be dissolved and transformed into nanofibers by controlling the reaction time. Samples were characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and high resolution transmission electron microscopy. The Bi 5 O 7 NO 3 nanofiber growth mechanism is discussed in detail. The band gap energy of the as-prepared Bi 5 O 7 NO 3 photocatalyst was about 2.70–2.90eV. Results of first-principle density functional theory calculations confirmed that Bi 5 O 7 NO 3 had a narrow band gap. They revealed that the conduction band bottom was predominantly composed of Bi 6s, Bi 6p, N 2p and O 2p orbitals, while the valence band (VB) top primarily consisted of Bi 6p, Bi 6s and O 2p orbitals. The as-obtained Bi 5 O 7 NO 3 nanofibers showed good photocatalytic activity and stability for the degradation of Rhodamine B (RhB) under visible light irradiation, which may be ascribed to the highly mobile conduction band (CB) and VB charge carriers.