BiOI photocatalyst was synthesized by a precipitation-filtration process and consequent hydrothermal treatment. The as-prepared BiOI exhibits efficient photocatalytic activity on the decomposition of widely used model pollutants, methyl orange (MO) and phenol, under visible light irradiation. Even under the illumination of a compact fluorescent lamp, the obtained BiOI also exhibits high photocatalytic activity. The possible photodegradation mechanism was studied by the examination of active species HO center dot, h(vb)(+), or O-2(-center dot) anions through adding scavengers such as tert-butanol (t-BuOH), I-anion, bromate anion and benzoquinone (BQ). The results show that photodegradation of MO molecules is attributed to the action of h(vb)(+) via direct hole oxidation process and the oxidation action of the generated O-2(-center dot) radicals. Dissolved oxygen play an important role in photocatalytic reaction, which could trap the photogenerated electrons to reduce the recombination of h(vb)(+) and e(cb)(-) and also function as a precursor of main oxidant O-2(-center dot). Hydroxyl radical was verified to be inappreciable for the decomposition of MO. (C) 2010 Elsevier B.V. All rights reserved.