A beta-cyclodextrin (beta-CD)-based copolymer (beta-CD maleic anhydride N-trimethylaminoethylmethacrylate chloride) with good thermal stability was designed and synthesized for flocculated decolorization of Reactive Brilliant Blue KN-R solutions. Jar tests indicated that with the optimal stirring mode as 120 rpm for 5 min and then 40 rpm for 5 min with a flocculant-to-dye ratio of 2 : 5 (w/w), a pH of 8-10, and a temperature of 20 degrees C, the maximum color removal reached. It is reported first in this article that, in addition to the polymer bridge and charge neutralization, the covalent bond of the reactive dye to the target flocculant molecules, which had a similar chemical structure to that of cellulose, contributed to the mechanism of flocculated decolorization. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 480-485, 2010