Uniform sphere-like cobalt (Co) nanosized particles (NPs) were synthesized by a solvothermal method, where ethylene glycol (EG) was used as solvent and ethylenediamine (EDA) as an additive. The spherelike Co NPs show high saturation magnetization, small remanent magnetizations and coercivities, which the saturation magnetization (237 emu/g) is higher than those reported in references. A composite (the Co NPs decorated on multi-walled carbon nanotubes (MVVCNTs)) was facilely fabricated via one-pot solvothermal method. The composite can be conveniently separated from aqueous solution by an external magnetic field. The pore size, surface area, and pore volume of the composite were determined to be about 2.37 nm, 15.33 m(2)/g, and 0.0731 cm(3)/g, respectively. The composite can be used to remove methyl orange (MO) from the aqueous solution, and the maximum adsorption capacity is about 170 mg/g, which is higher than those reported in the References. (C) 2015 Elsevier Ltd. All rights reserved.