Interest in desalination using membrane processes has increased with the growth of membrane science and technology. Fouling of ion exchange membranes is one of the most significant considerations in the operation of the electrodialysis desalination process. The influence of the adsorption capacity of foulants on the fouling potential was investigated in an electrodialysis desalination process in the presence of negatively charged organic foulants, humate, bovine serum albumin and sodium dodecylbenzenesulfonate (SDBS). The SDBS showed higher adsorption capacity on the anion exchange membrane surface than the other two foulants in the adsorption equilibrium experiments. Of three different organic foulants, the SDBS had a more severe fouling effect on the process performance in the electrodialysis desalination of synthetic brackish water, with irreversible fouling due to the high adsorption capacity. The study clearly showed that the adsorption capacity affects the fouling potential of the electrodialysis desalination process.