A simple method for the preparation of magnetic nanocomposites consisting of cobalt ferrite (CF; CoFe2O4) nanoparticles, polybenzoxazine (PB), linear low-density polyethylene (LLDPE), and linear low-density polyethylene-g-maleic anhydride (LgM) is described. The composites were prepared by the formation of benzoxazine (BA)-CF nanopowders followed by melt blending with LLDPE and the thermal curing of BA. The composites were characterized by X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, universal testing machine measurement, and vibrating sample magnetometry. The composites consisting of LLDPE, PB, and LgM (47.5L-47.5PB-5LgM) exhibited a higher tensile strength (23.82 MPa) than pure LLDPE and a greater elongation at break (6.11%) than pure PB. The tensile strength of the composites decreased from 19.92 to 18.55 MPa with increasing CF loading (from 14.25 to 33.25 wt %). The saturation magnetization of the composites containing 33.25 wt % CF was 18.28 emu/g, and it decreased with decreasing amount of CF in the composite. The composite films exhibited mechanical flexibility and magnetic properties. © 2012 Wiley Periodicals, Inc.