The performance of the electrolytic decolorization of dyestuff was evaluated with a bipolar packed bed cell (BPBC) using an aqueous solution of Reactive Brilliant Red X-3B as a model compound. The color of this azo dye can be removed satisfactorily for most of the conditions tested. The decolorizing load (DL) and specific energy consumption (SEC) were used as indicating parameters. The DL decreases with the increase of packed layers, is indifferent to solution pH but increases with cell voltage, water flowrate, dye initial concentration, and addition of NaCl. The SEC increases with the packed layers, the voltage, dye initial solution, solution conductivity and decreases with water flowrate. The mechanism of decolorization was found to be the cleavage of the conjugated double bonds and the destruction of unsaturated system of dye stuff. (C) 2003 Elsevier B.V. All rights reserved.