The physiological activities and functional properties of chitosan oligomers depend on their molecular weight and chain length. Therefore, it is important to produce these bio-ingredients with a high degree of purity and homogeneity. Electrodialysis with ultrafiltration membrane (EDUF), a new method for separation of organic charged molecules at large scale, was tested. The effect of the molecular weight cut-off (MWCO) of the ultrafiltration membrane stacked in the electrodialysis (ED) cell was studied as well as the performances of the process in terms of oligomer migration rate and electrodialytic parameters. Electromigration rates of the chitosan oligomers varied between 1.05 and 14.45% expressed as a percentage of the initial content in the feed solution depending on the operating conditions (membrane MWCO and processing time). Contrary to the 20,000 Da MWCO UF-membrane which was permeable to all chitosan oligomer, the 500Da MWCO UF-membrane did not exhibit any permeability. The 1000 Da membrane was selective to the tetramer during 3 h of operation, whereas the 5000 and 10,000 Da membranes were selective to the tetramer during the first 2 h of the treatment. It was demonstrated in this study the effectiveness of EDUF for the electroseparation of chitosan oligomers. (C) 2007 Elsevier B.V. All rights reserved.