The adsorption and transport characteristics of natural organic matter (NOM) in an ion-exchange (IX) membrane were investigated and the various methods to characterize the properties of NOM and the IX membrane were collectively evaluated in this study. NOM adsorption by an IX membrane is affected by both pH and ion strength. Under alkaline pH and low ionic strength, greater NOM adsorption can be expected. A good relationship was obtained between the amount of adsorbed NOM and the zeta potential. The NOM acids constituents are expected to be transported preferentially through an IX membrane during the electrodialysis (ED) process because of their negative charge density. However, the molecular mass of the NOM acids was too high to allow them to pass through the IX membrane pores, and this caused an accumulation or adsorption of the solutes on the membrane surface. A fractional-rejection method was applied to determine the apparent pore size distribution of IX membranes and the selectivity coefficient was used to calculate apparent charges ofNOM. The major apparent pore size distribution (PDS) of the IX membrane used in this study lay in the range 100-200 mass units. The apparent charge of the NOM used was 5.5 (dimensionless).