Membrane filtration processes, due to their great performance, have been recognized as one of the effective technologies for the reclamation of wastewater, especially for the removals of inorganic/organic micropollutants and wastewater effluent organic matter (EfOM). Although the attraction of membrane filtration is remarkable, membrane fouling is a major obstacle to its usage; thus, the degree of fouling can have a significant impact on the cost, design and operation of full-scale facilities. In this study, the propensity for membrane fouling by EfOM was investigated using a flow field-flow fractionation (FIFFF) technique by comparing two different nanofiltration (NF) membranes: meta-phenylene diamine (MPD) versus piperazine based polyamides. From the characterizations of EfOM with FIFFF, the mutual interaction between the membrane surface and solutes was elucidated from the shape of elution peak and the hydrodynamic sizes with respect to the different membrane properties. Therefore, the propensities for fouling of the two NF membranes by EfOM were evaluated in relation to the membrane characteristics. Finally, several indicators of the potential for membrane fouling have been suggested in this study. This FIFFF technique can not only characterize the physicochemical properties of EfOM based on certain membrane properties, but can also provide a quick and easy evaluation of the potential for membrane fouling in terms of the suggested indicators. Furthermore, this technique is expected to contribute to the optimal design of membrane systems through the optimum selection of membranes for water and wastewater treatment. (C) 2010 Elsevier B.V. All rights reserved.