To increase the water solubility and cationic charges at pH 7, cationic moieties were introduced onto both the C-6-OH and C-2-NH2 groups in the chitosan (CTS) matrix by graft modification. The chemical structure of the obtained copolymer was demonstrated by characterizations of FT-IR. C-13 NMR, WXRD, SEM. Its excellent decolorization properties as a novel fiocculant were evaluated with the C.I. Reactive Orange 5 (RO 5) and C.I. Reactive Blue 19 (RB 19) solutions using a jar test method. Both the nature of the anionic dyes and the pH of the initial dye solutions had effects on the decolorization properties. Charge neutralization played a dominant role for the color removal at pH 4, while polymer bridging contributed mainly to the color removal at pH 7. For the given flocculant/dye solutions, added salt was not in favor of the flocculated decolorization. At 25 degrees C, the flocculant needed for the highest color removal at pH 4 was 60 wt% of the dye (RO 5 or RB 19), but that at pH 7 were 100 wt% of RB 19 and 120 wt% of RO 5, respectively. (C) 2010 Elsevier B.V. All rights reserved.