The ZnO-mediated photocatalysis process has been successfully applied to degradation of commercial dye, Cl Reactive Blue 160 (RB 160). Eleven reaction intermediates were separated, identified and characterized by the GC-MS techniques, giving insight into mechanistic details of the ZnO-mediated catalysis process under UV irradiation and the pathways of degradation process. The degradation process take place through competitive reactions such as destruction of chromophoric group, hydroxylation of the aromatic ring, substitution on aromatic ring, desulphonation, decarboxylation and further ring opening to give aliphatic compounds. Smaller aliphatic compounds formed during the process were identified by IC, while the triazine group and naphthalene group containing compounds remains intact even after decolorization for a prolonged time due to high resistance to oxidation. The probable degradation pathways were proposed and discussed. (C) 2011 Elsevier B.V. All rights reserved.