Abstract: Without any other auxiliaries, a β-cyclodextrin (β-CD) based cationic polyelectrolyte with improved hydrophobicity (P(β-CD-MAH-co-AETAC-co-St)) was synthesized by means of aqueous solution polymerization, using ammonium persulfate (APS) and sodium bisulfite (SBS) as initiators and the derivative of β-CD (β-CD-MAH), acryloyloxyethyl trimethyl ammonium chloride (AETAC) and styrene (St) as monomers. The chemical structure and properties of P(β-CD-MAH-co-AETAC-co-St) were characterized by 1H-NMR, cationic degree, intrinsic viscosity and solution surface tension. The performance of flocculated decolorization of P(β-CD-MAH-co-AETAC-co-St) was investigated in anionic dye of reactive brilliant blue (KN-R) solutions. Results showed that P(β-CD-MAH-co-AETAC-co-St) had faster decolorization speed for the dye solution; the dosage of flocculant reduced when it reached the highst decolorization rate; the ranges of pH of dye solution and the dosage of flocculant widened when it reached a relative high decolorization rate; the anti-salt property improved. Moreover, for the given flocculant-dye solutions, the interactions between flocculant molecular and dyestuff molecular existed relatively notable hydrophobic interaction part from the interactions, e.g. charge neutralization.