Copolymer of acrylamide and 2-[(methacryloyloxy)ethyl]trimethylammonium chloride [P(AM-DMC)] is found to be effective to combine anionic dyes with strong aqueous solubility. This work aims mainly at revealing the interaction between anionic dyes and [P(AM-DMC)] by running jar test, spectra analysis and equilibrium dialysis experiments. The results show that P(AM-DMC) effectively decolorizes the tested strong water soluble anionic dyes, such as acidic, reactive and direct dyes, from their aqueous solutions under mild acidic and neutral conditions. Higher cationicity and optimal dose of flocculant P(AM-DMC) have to be used to achieve satisfactory and effective decolorization. Comparison of IR spectra of dye, flocculant P(AM-DMC) and the floc formed indicates chemical interaction occurred between sulfonic groups of dye and quaternary ammonium of flocculant. Plots of r-log C suggest cooperative interaction exists evidently for some dyes tested. Addition of KCl or urea reduces binding extent evidently, which shows the importance of electrostatic and hydrophobic interaction. Therefore the interaction between dyes tested and P(AM-DMC) might be controlled by hydrophobic, cooperative interaction and energetic interaction which includes chemical and electrostatic interactions. (c) 2006 Elsevier B.V. All rights reserved.