The photooxidative degradation of 4-nitrophenol (4-NP) was studied in the UV/H2O2 process. The effects of applied H2O, dose, initial 4-NP concentration and UV light intensity have been studied. Degradation was complete in 13 min and follows apparent first-order kinetics. The removal efficiency of 4-NP depends on the operational parameters and increases as the initial concentration of H2O2 and light intensity are increased but it decreases when the initial concentration of 4-NP is increased. From HPLC analysis, major intermediate products were hydroxyl derivative,9 of 4-NP as a result of photooxidative hydroxylation. (c) 2006 Elsevier B.V. All rights reserved.