Under galvanostatic mode，the decolorization behavior of Reactive Blue 19，one of anthraquinone dyes，was studied by using activated carbon fiber（ACF）as anode and cathode in paired electrolysis in an undivided cell.The relationship between decolorization mechanism and current density was investigated.In the range of 0—0.1 mA·cm-2，decolorization resulted from adsorption of the dye on ACF，and adsorption behavior was scarcely affected by the current density.The color removal was about 15%.In the range of 0.2—0.6 mA·cm-2，anodic electrooxidation and cathodic adsorption of the dye played important roles in decolorization.The maximum color removal was 52%.In the range of 0.7—1.0 mA·cm-2，the paired electrolysis of the dye on anode and cathode filled the role of decolorization.The color removal might be up to 83%.