In this work, the degradation of 4-chlorophenol (4CP) under simultaneous microwave assisted UV (electrodeless discharge lamp) photocatalysis technique (MW/UV/TiO2) was investigated. Several factors affecting the degradation of 4CP by MW/TJV/TiO2 method, such as the dosage of photocatalysts, the initial pH value of the solutions, gas bubbling, light intensity and addition of H2O2 oxidant, were studied in detail. The synergistic effects between microwave irradiation and TiO2 photocatalysis were also studied. The major intermediates were found to be chlorobenzene, phenol, hydroquinone, benzoquinone and 4-chlorocatechol. Based on the results, a general reaction pathway for the degradation of 4CP was proposed. (c) 2005 Elsevier B.V. All rights reserved.