Ag-modified BiOBr composite photocatalysts were prepared via a simple phase-transfer methodology and used for cleanup of Rhodamine B (RhB) aqueous solution under visible light irradiation. X-ray diffraction, ultraviolet-visible diffuse reflectance spectra (UV-Vis-DRS) and high resolution X-ray photoelectron spectra characterizations confirmed the Ag-modification significantly affected the optical property, structures and reactivity of the BiOBr-based photocatalysts. In the Ag-modification process, a large portion of Ag+ may extract Br1- from BiOBr and the as-formed AgBr epitaxially located along the {102} crystal surface of BiOBr. The rest Ag+ will be either photo-reduced by methanol into Ag-0 or form Ag2O. In nature, the Ag-modified BiOBr materials are multi-junction photocatalysts of Ag/Ag2O/AgBr/BiOBr. The Ag-modification can greatly enhance the absorption of visible light but deteriorates the photocatalytic activity in comparison to the primitive BiOBr in visible-light-driven photodegradation of RhB. The activity of RhB photodegradation on such catalysts is inversely proportional to AgBr loading within 0.2-2.0 wt% region. Such unusual photocatalytic performance was tentatively attributed to the special band structure of the materials.