Degradation efficiency and detoxification of Diclofenac (DCF) in Fe-MCM-41/O-3 process were evaluated in this study. Both O-3 and Fe-MCM-41/O-3 systems were effective for DCF removal and the presence of Fe-MCM-41 significantly enhanced its mineralization. High mineralization efficiency (76.3%) was achieved in Fe-MCM-41/O-3 process, 2.8 times higher than that in ozonation. Hydroxyl radicals were found to be the main active species and they were generated via the surface reaction of Fe-MCM-41 and O-3. Intermediates were detected in Fe-MCM-41/O-3 process and a possible degradation pathway was proposed. Dehalogenation, hydroxylation and cleavage of the NH-bridge between the aromatic rings were found in the degradation process. Formic acid, acetic acid, oxalic acid were also detected and their accumulation in catalytic ozonation process was less than that in ozonation as a result of more generation of (OH)-O-center dot. What' s more, small molecular carboxylic acids accounted for 70% of the remaining TOC in catalytic ozonation process, only 32.5% in sole ozonation process. Toxicity assessments were conducted using chlorella according to standard procedure. The intermediates accumulated in the first 15 min were more toxic than its initial status. It had a high level of detoxification after 30 min treatment. (C) 2016 Elsevier B.V. All rights reserved.