Bench-scale laboratory experiments were conducted using broad spectrum UV-A to induce TiO2-based photocatalytic treatment of monochlorobenzene under aerobic and anaerobic conditions. Previous photolytic-based studies conducted on chlorinated aromatics support the decomposition pathway of de-halogenation followed by cleavage of the aromatic ring due to attack by OH radicals. However, in this study of anaerobic degradation, GC-MS and HPLC analyses of intermediate by-products accumulated on the catalyst surface indicate that chlorophenols (o-, m-, p-) are the predominant species rather than benzene or phenol, and that dechlorination proceeds after ring cleavage. (C) 2006 Elsevier B.V. All rights reserved.