In this study, a two-stage ultrafiltration (UF) membrane separation process on a pilot scale was introduced to resolve the shortcomings caused by the application of salt precipitation technique in the conventional process of Reactive Brilliant Blue KN-R production. The first stage was used for diafiltration and concentration of dye solution, and the second stage was applied to recover the dye from permeate of the first stage. Both the operating pressure and cross-flow velocity had significant and moderate effect on the permeate flux (24.9 to 129.7 L.m(-2).h(-1)) and salt rejection (26.9%-55.7%), but insignificant effect on dye rejection since the rejections were always higher than 99.5%. The two-stage UF membrane process exhibited good performance as the dye and salt concentrations in concentrate of first stage were 203 and 5.4 g/L, and 67.1% of salt could be removed and the dye loss was negligible (0.1%) in the whole process. For a dye plant with a capacity of 1000 ton per year, the preliminary economic evaluation of an UF plant based on pilot scale showed that the cost of every ton of Reactive Brilliant Blue KN-R was US $154. (C) 2011 Elsevier B.V. All rights reserved.