Dissolved organic nitrogen (DON) in water is associated with disinfection by-products (DBPs) formation especially for nitrogenous DBPs (N-DBPs), which possess stronger adverse health effects than traditional carbonaceous DBPs (C-DBPs). DON characteristics affect not only the amount but also the speciation of DBPs formation. To characterize DON constituents in water, this study modified and validated a DON fractionation method using DAX-8, XAD-4, and MSC-1H resins. The method was then used to investigate the characterization and composition of DON constituents in treated wastewater effluents and raw waters. From validation tests using nitrogenous surrogate solutions, recoveries of each pretreatment step as well as selected eluents and flow rates were acceptable for fractionation of aqueous DON. The absence of any statistically significant difference in DON compositions between duplicate treated effluents also validated the applicability of the modified fractionation method for field water. The proposed method will be useful for characterizing and evaluating the properties, amounts, and compositions of DON-enriched materials in water and help address the current lack of information on DON profiles in water sources. (C) 2013 Elsevier B.V. All rights reserved.