Removal of dyes from the industrial discharge water is an important issue for safety of the environment. In this study, magnetic (magnetite, Fe3O4) nanoparticles were coated with chitosan (CS) and the efficiency of these chitosan coated magnetic nanoparticles (Fe3O4-CS) for the adsorption of a reactive textile dye (Reactive Yellow 145, RY145) was examined first time in literature. TEM, XRD, and EPR results revealed that the thickness of the coat was about 25 nm, no phase change in the spinel structure of magnetic particles existed after coating, and particles had paramagnetic property, respectively. Adsorption of RY145 on Fe3O4-CS nanoparticles occurs according to Langmuir model in the temperature range 25 degrees C-45 degrees C with a maximum adsorption capacity of 47.62 mg g(-1) at 25 degrees C, in aqueous media. Thermodynamic parameters demonstrated that the adsorption process was endothermic and spontaneous, and the maximum desorption of the dye was 80% over a single adsorption/desorption cycle. In this study, the high efficiency of the CS coated magnetic nanoparticles in the adsorption and removal of reactive dyes from water was shown on model RY145. This type of nanoparticles can be good candidates in industrial applications for the decolorization of waste waters. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012