The performance of ultrafiltration (UF) and nanofiltration (NF) membranes on disinfection by-products (DBPs) precursor removal in a surface water having low-to-medium dissolved organic carbon (DOC) and specific ultraviolet absorbance (SUVA(254)) levels was evaluated. While higher molecular weight (HMW) DOC fraction was successfully rejected (> 90%), lower molecular weight (LMW) fraction could be removed only 1.5-30% by the tested four different membranes (two UF and two NF). This finding suggested that although NF and UF membranes with pore sizes of <= 1000 Da are highly effective on the removal of HMW NOM from waters having low-to-medium DOC and SUVA(254) levels, such membranes are not effective in these waters in rejecting LMW fractions (i.e., < 2000 Da). NF membranes provided THM and HAA formation reductions above 90%. However, DOC and UVA(254) rejections could not be directly linked to DBP formation reductions by the tested membranes. Due to higher rejection of DOC than the bromide ion in UF and NF separation, Br/DOC ratio increased which further increased the relative occurrence of brominated THM and HAA species over chlorinated ones. (c) 2008 Elsevier B.V. All rights reserved.