The degradation kinetics and pathways of chlortoluron during UV irradiation and UV/chlorine process as well as the formation of disinfection by-products (DBPs) after post-chlorination were investigated in this study. The quantum yield of chlortoluron was calculated as 0.0258 mol einstein(-1) and the effect of solution pH was negligible during UV irradiation. On the other hand, the degradation rate of chlortoluron during UV/chlorine process was significantly promoted at acidic conditions as well as high chlorine doses and UV intensity. UV irradiation and UV/chlorination of chlortoluron both followed the pseudo-first order reaction kinetics, but UV/chlorine process is more efficient than UV irradiation with the reaction rate constant between chlortoluron and OH radicals determined as (2.18 +/- 0.83) x 10(9) M-1 s(-1). The mineralization of chlortoluron was considerably increased with increasing chlorine dose and decreasing pH during UV/chlorine process. The degradation pathways of chlortoluron during UV irradiation and UV/chlorine processes were proposed according to the identified intermediates. The formation of carbonaceous DBPs (C-DBPs) and nitrogenous DBPs (N-DBPs) during direct chlorination and post chlorination of UV irradiation and UV/chlorine processes were investigated as well. More DBP precursors were formed during UV/chlorine process compared to direct chlorination and UV irradiation, which deserves extensive concerns in drinking water treatment processes. (C) 2015 Elsevier B.V. All rights reserved.