A cationic organic flocculant epichlorohydrin-dimethylamine (EPI-DMA) was employed for the treatment of acid and direct dye. The study aims at investigating the flocculation performance of EPI-DMA for the model dye, and corresponding floc aggregation properties, which were determined by jar test and photometric dispersion analysis, respectively. The interactions between cationic flocculant and anionic dye were investigated through spectra analysis. The results showed that EPI-DMA effectively decolorized the tested acid and direct dye. The viscosity and cationicity of EPI-DMA had different influence on the removal of different dye. Chemical interaction was observed between quaternary ammonium of EPI-DMA and sulfonic group of dye. The flocculation dynamic process showed that flocs with better aggregation and sedimentation properties were produced by EPI-DMA with higher viscosity and cationicity for acid dye. Contrarily, flocs with the best aggregation and sedimentation properties were produced by EPI-DMA with the lowest viscosity and cationicity for direct dye. (C) 2011 Elsevier Ltd. All rights reserved.