A series of Bi-based oxyiodide photocatalysts with different compositions were synthesized via a precipitation-filtration process followed by hydrothermal treatment. The compositions of the bismuth oxyiodides could be controlled by adjusting the precipitation pH values. The effects of the precipitation pH values on the compositions and photocatalytic activities of the bismuth oxyiodides were investigated and the relationship between structure and photocatalytic property is discussed. All the as-prepared powders exhibit photocatalytic activity on decomposing methyl orange under visible light irradiation. The activity increases with increasing content of iodine in the bismuth oxyiodides. (C) 2010 Elsevier Ltd. All rights reserved.