An electro-ultrafiltration process was proposed and developed for concentrating protein solution rapidly by applying an electric field and employing a membrane with a higher nominal molecular weight cut-off (NMWCO) than the molecular weight of protein to be concentrated. In this process, the high NMWCO membrane was used to achieve a high permeate flux while the adoption of an electric field was used to obtain a high rejection of the target protein by manipulating the electrophoretic effect. Bovine serum albumen (BSA) was used as a model protein, and 50 and 100 kDa NMWCO polysulphone (PS) membranes were used for BSA concentration. The effects of membrane NMWCO, electric field strength, feed concentration on permeate flux and protein rejection were examined. The experimental results showed that the concentration time required for a target protein concentration could be significantly shortened when an electric field was applied and a membrane with higher NMWCO was used. When a 3000 V m(-1) electric field was applied and the 100 kDa NMWCO polysulphone (PS) membrane was used, the concentration time for concentrating 0.5 g L-1 BSA solution to around 1.0 g L-1 decreased by 80% as compared with the process with a 50 kDa membrane without electric field, suggesting that this electro-ultrafiltration concentration process is a viable alternative to conventional ultrafiltration process and a promising method for concentrating dilute protein solutions. (C) 2010 Elsevier B.V. All rights reserved.