Membrane process has increasingly developed as a reliable and effective means of improving product yield and reducing manufacturing costs in the reactive dye industry. In order to improve a product's quality, ultrafiltration (UF) membrane has been applied to perform Reactive Brilliant Blue KN-R desalting and concentration. The performance of this membrane's separation process was evaluated under different operating conditions, through which the influence of operating pressure, temperature, cross-flow velocity, pH, concentration of feed and operating time on permeate flux, rejection of Reactive Brilliant Blue KN-R and sodium sulfate were studied. When the permeate flux reached 63.2 L m(-2) h(-1) at ambient temperature, the rejection of Reactive Brilliant Blue KN-R was over 99.0% and the rejection of sodium sulfate was less than 50.0%. And operating pressure, temperature, cross-flow velocity and concentration of feed have posed significant influence on the membrane's separation performance, whereas pH and operating time had little effect on the separation performance. This study also illustrates that membrane process is a promising technique for Reactive Brilliant Blue KN-R desalting and concentration. (c) 2008 Elsevier B.V. All rights reserved.