Magnetic nanoparticles prepared with iron oxides and N-benzyl-O-carboxymethylchitosan, an amphiphilic chitosan derivative, were prepared through the incorporation method and characterized by Fourier infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), Mossbauer spectroscopy, and magnetization measurements. The gamma-Fe2O3 nanoparticles proved to be spherical and well crystallized, and some aggregation behavior was observed. The particles containing the polymer presented saturation magnetization of 18.4 emu g(-1) and roughly superparamagnetic behavior. The material was used to adsorb three cationic dyes from aqueous solution (methylene blue, crystal violet, and malachite green). The adsorption process preferably followed the Langmuir-Freundlich isotherm and pseudo-second-order kinetic model. The removal of the dyes was optimized using a 32 factorial design, and the initial dye concentration proved to be more influential in dye adsorption than the temperature of the system. (C) 2011 Elsevier B.V. All rights reserved.