Owing to the unique microporous structure and high specific surface area, activated carbon (AC) could act as a good carrier for functional materials. In this paper, CoFe2O4/AC nanocomposites were prepared by a facile hydrothermal method for the adsorption of dyes in wastewater. The results indicated that CoFe2O4 nanoparticles presented the spinel structure and existed in the pores of AC. The saturation magnetization (Ms) increased with the CoFe2O4 content, while the surface area and pore volume decreased. For the larger magnetic moment, very few CoFe2O4 were needed to maintain the higher surface area of CoFe2O4/AC nanocomposites. The sample-5 (CoFe2O4:C = 1:200) possessed the surface area of 1096.85 m(2) g(-1) (close to 1243.35 m(2) g(-1) of AC) and Ms of 5.11 emu g(-1), which were sufficient for magnetic separation in wastewater treatment. 99% methylene blue could be adsorbed in 50 min, and then the CoFe2O4/AC nanocomposites could be separated from the solution easily by an outer magnet. (C) 2014 Elsevier B.V. All rights reserved.