An important issue in chlorine drinking water disinfection is the generation from natural organic matter (NOM) of disinfection by-products (DBPs), especially trihalomethanes (THMs). The THMs generation can be limited by reducing the levels of NOM prior to the chlorination step. Herein, photo-Fenton system under solar simulator degraded humic acid solutions (as NOM model compounds), as well as NOM contained in river water (Pance River, Cali-Colombia), and dramatically reduced THMs formation during the subsequent chlorination step. In both cases the initial pH of treated water was near to 7.In no pre-treated river water 100-160 mu g/L of THMs are formed during chlorination while values of 20-60 mu g/L were reached in water previously treated for 4 h by neutral photo-Fenton under solar simulator. The decrease in the generated THMs/total organic carbon ratio suggests that mainly the NOM fraction sensitive to THMs formation was photo-degraded. Therefore, the neutral photo-Fenton reagent could be implemented as a technological option for NOM removal for limiting THMs formation during a subsequent chlorination step. (C) 2011 Elsevier B.V. All rights reserved.