Mesoporous magnetic Co-NPs(nanoparticles)/carbon nanocomposites were synthesized by carbonization of polyacrylonitrile (PAN) microspheres entrapped with cobalt salt for the first time. The structure and morphology of the porous magnetic nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and N-2 adsorption-desorption technique. The nanocomposites possess very high saturation magnetization (Ms is up to similar to 133 emu/g), near-zero remanence, and very low coercivity (Hc is down to similar to 0.023 KOe). Meanwhile, the nanocomposites have mesoporous structure with average pore size of 4 nm and high specific surface area of 232 m(2)/g, which can be tuned by changing the carbonization conditions. Using methyl orange (MO) as model pollutant in water, the mesoporous magnetic nanocomposites showed good adsorption capacity of 380 mg/g, and the absorbed MO could be easily released in ethanol. The mesoporous nanocomposites were facile separated from solution under external magnetic force, and over 85% adsorption capacity for MO could be retained after five adsorption/desorption cycles. (C) 2012 Elsevier Inc. All rights reserved.