The photodegradation of aqueous solutions of C.I. Reactive Orange 16 was investigated under UV irradiation. The degradation was studied by monitoring the change in absorption and relative intensity employing UV-spectroscopic and GC/MS analysis as functions of irradiation time. The rate of degradation of the dye was evaluated. The solution was completely decolorized after 100 min of photooxidation. The generated degradation products were detected by GC/MS. 6-Acetylamino-3-amino-naphthalene-2sulfonic acid, N-(3,4-bis-hydroxymethyl-phenyl)-acetamide and plithalic acid were found during the degradation of C.I. Reactive Orange 16. The probable pathways for the formation of the degradation products were proposed. GC/MS analysis and degradation pathways demonstrated that naphthalene and benzene rings were observed during photooxidation. (C) 2004 Elsevier Ltd. All rights reserved.