BiOBr hierarchical structures were successfully synthesized through a solvothermal process assisted with citric acid using methanol as a solvent. The as-synthesized BiOBr hierarchical structures have diameters of ca. 1 mu m, and assembled by numerous porous nanosheets with exposed (110) facets. Results indicated that the crystal growth and morphology structures of BiOBr were significantly influenced by the amount of citric acid, the solvothermal time and the solvent used in reaction. In addition, the as-synthesized BiOBr hierarchical structures exhibited high photocatalytic activity on the degradation of methyl orange under either UV light or simulated sunlight illumination, due to the larger specific surface area and unique hierarchical structures assembled by numerous BiOBr porous nanosheets.