In this work, hydrophobic magnetic polyaniline nanocomposite (PAni/Fe3O4/C) was prepared by insitu emulsion polymerization of aniline in the presence of magnetic carbon. Magnetic nanocomposites were characterized by FT-IR spectra, X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Brunauer-Emmett-Teller (BET) method was utilized to measure specific surface area and pore size distribution of magnetic nanocomposites. The water contact angle values for both magnetic nanocomposites indicated high hydrophobic properties for PAni/Fe3O4/C. PAni/ Fe3O4/C was evaluated for removal of diesel oil from seawater by magnetic separation. Separation capacity (g/g) was governed by separation time, magnetic nanocomposite dose as well as initial oil concentration. Kinetic studies showed that oil separation process followed pseudo-second-order model. Thermodynamics studies of oil sorption process were investigated at temperature range (283 K-323 K) and indicated endothermic, spontaneous and random behavior. The reusability of magnetic polyaniline sorbent was carried out for ten cycles. (C) 2016 Elsevier Ltd. All rights reserved.