We present a surfactant-mediated approach to the production of single-crystal Bi 3 O 4 Br nanorings via a simple solvothermal method. The ring-like morphology is rare among bismuth oxyhalides, and the reaction pathways are superior to traditional chemical transformations. In detail, Bi 3 O 4 Br nanorings are prepared in three stages: (1) the formation of precursors, (2) selective etching and (3) Ostwald ripening. During these steps, the extra usage of templates is avoided and a series of useful intermediates are obtained. Besides, this method can be extended to fabricate other bismuth oxyhalide nanorings. Under visible-light irradiation, all of our samples are photo-activated. The Bi 3 O 4 Br nanorings exhibit an efficient oxygen-evolution rate (72.54 μmol h -1 ) and pollutant degradation rate (4.71 × 10 -2 g min -1 m -2 ), which can be attributed to their unique ring structures and band potentials. Thus, the surfactant-mediated chemical conversion strategy not only paves a new way to enhance the photocatalytic activity of bismuth oxyhalides, but also provides an important large-scale route for designing other nanomaterials with ring-like structures.