BiOCl_xBr_1−x catalysts were synthesized through an alcoholysis method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and diffuse reflectance spectroscopy (DRS). The as-prepared photocatalysts were found to be tetragonal crystal structure and lamellar plate morphology. Their band gaps were between 3.44 and 2.83 eV. The effect of light response on the photocatalytic activity of BiOCl_xBr_1−x was investigated by degradation of Rhodamine B (RhB). Complete removal of RhB from water was realized under simulated sunlight irradiation for 50 min with BiOCl_0.5Br_0.5. Mechanism studies showed that photogenerated holes and superoxide anion radicals played important roles in RhB photodegradation. The results of chemical oxygen demand (COD) confirmed RhB mineralization. The effect of light response on the activity of BiOCl_xBr_1−x was further investigated under monochromatic light irradiation, and BiOCl_0.5Br_0.5 catalyst exhibited the highest activity. Furthermore, BiOCl_0.5Br_0.5 exhibited high stability, suggesting its practical application for the removal of RhB pollutant from water.