This present work describes the preparation and adsorption behavior of Fe3O4 magnetic nanoparticles (MNPs) modified with 3-glycidoxypropyltrimethoxysilane (GPTMS) and glycine (Gly). The magnetic nanoparticles which can excellently remove both anionic and cationic dyes in severe environment (highly acidic or strong alkaline) were synthesized by a simple method. The MNPs were characterized by transmission electron microscopy (TEM), X-ray diffraction, infra-red (IR) spectra, and thermogravimetric analysis (TGA). We investigated organic dye uptake capacity of Fe3O4@GPTMS@Gly as a function of contact time, dye concentration and pH. Furthermore, adsorption isotherms and kinetics were studied to understand the adsorption mechanism of the MNPs. In addition, desorption of the MNPs was carried out by adjusting pH with HCl or NaOH solution. The adsorbent can effectively remove both anionic and cationic dyes from aqueous solution and shows reusability and high separation efficiency. (C) 2013 Elsevier B.V. All rights reserved.