The biosorption ability of sugar-beet pulp was improved by modifying with quaternary ammonium-salt for examination of its potential application in decolorization process from wastewater. Decolorization conditions were investigated as functions of different experimental parameters such as initial pH, biosorbent amount, time and dye concentration. At the optimum pH (2.0) the biosorption reached to an equilibrium within relatively short time (30 min) and was followed by the pseudo-second-order kinetic model. Langmuir isotherm better fitted the equilibrium data with the maximum monolayer biosorption capacity of 98.32 mg g(-1). AR1 biosorption performance of quaternary ammonium-salt modified sugar-beet pulp (QAMSBP) was also investigated in the mix solutions containing RB49 and AY17 dyes at different concentrations (1, 50 and 100 mg L-1) and the biosorption potential of QAMSBP did not change at 1 and 50 mg L-1 of other dyes. Obtained results demonstrated that AR1 biosorption onto QAMSBP could also be successfully applied to real wastewater in continuous system. IR analysis revealed the complexation is one of the important mechanisms involved in AR1 biosorption. All the results indicated that QAMSBP was a potential biosorbent for toxic dye removal from wastewaters. (C) 2014 Elsevier B.V. All rights reserved.