Well-defined bismuth oxyhalide hierarchical microflowers with rich oxygen vacancies (named BiO_1−xCl hierarchical microflowers) were prepared by a simple solvothermal strategy. The BiO_1−xCl hierarchical microflowers showed excellent photocatalytic properties for the degradation of typical organic dyes and antibiotics under visible light irradiation, compared with pure BiOCl hierarchical nanomaterials. Excitingly, this superior photocatalytic activity was maintained for decomposing the complex ternary mixed antibiotics. Almost 100% antibiotics can be photodegraded within 30 min in the ternary mixed antibiotic solution. This high photocatalytic activity originates from the bulk defects of hierarchical microflowers.