This work presents the preparation and photocatalytic activity of BiOX (X = Cl, Br), it is feasible to prepare BiOX by the hydrolysis of BiX3 (X = Cl, Br). Both BiOCl and BiOBr show photocatalytic activity for the photodegradation of azo dyes (methyl orange and congo red) under the simulated sunlight. We have measured the HO center dot generated in the above process by terephthalic acid indirectly. Both BiOCl and BiOBr have been characterized by XPS, DRS. SEM, TEM, XRD and xi potential. XPS data indicate that the surfaces of the BiOX samples are covered by low amounts of adsorbed azo dye molecules or/and intermediates produced during the dye photodecomposition. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.