A comprehensive study of the degradation of linuron, one of the phenylurea herbicides, was conducted by using different treatment processes including UV, zonation and UV/O-3. The effect of various anions on the performance of ozonation has been examined. N-terminus demethoxylation, photohydrolysis with or without dechlorination, and N-terminus demethylation have been found to be the major mechanisms in the linuron decay under the irradiation of UV at 254 nm while N-terminus demethoxylation, dechlorination and hydroxylation on benzene ring was observed to be involved in the zonation process. Eight new intermediates were identified in UV process in this study compared with previous studies. Different decay pathways were proposed based on the identified intermediates in the three studied processes. UV/O-3 has demonstrated the best performance among these three processes in terms of LNR decay, mineralization, dechlorination and de-nitrogenation. (C) 2010 Elsevier B.V. All rights reserved.