Textile industries are one of the main sources of water pollution. Wastewater containing dyes present a serious environmental problem because of its high toxicity and possible accumulation in the environment. Azo dyes are the main class of dyes among all dyes. In the present work, functionalized multi walled carbon nanotubes (f-MWNTs) have been used for the adsorption (decolorization) of three different azoic dyes. Multiwalled carbon nanotubes (MWNTs) were synthesized by chemical vapor deposition (CVD) technique and purified by air oxidation and acid treatment. These purified MWNTs were further functionalized by acid treatment. Different characterization techniques like Electron microscopy, Raman and FTIR spectroscopy have been used to study the adsorption of azoic dyes over f-MWNTs surface. UV-visible absorption spectroscopy was used to quantify the decolorization of dyes. Adsorption isotherm and kinetic behaviors of f-MWNTs for azoic dyes removal were studied and fitted to different existing models. Maximum adsorption capacity of 148, 152 and 141 mg/g was obtained for direct congo red, reactive green HE4BD and golden yellow MR dyes, respectively. In addition effect of initial pH of dye solution and initial concentration of dye solution on adsorption property of f-MWNTs were studied. (C) 2010 Elsevier B.V. All rights reserved.