Hard magnetic BaFe12O19 (BaFe) nanoparticles were synthesized via a facile sonochemical-assisted reaction. BaFe nanoparticles were then added to acrylonitrile-butadiene-styrene (ABS) and cellulose acetate (CA) in order to make magnetic nanocomposite. Nanoparticles and nanocomposites were then characterized using X-ray diffraction. Scanning electron microscopy and Fourier transform infrared spectroscopy. The magnetic properties of the samples were also investigated using an alternating gradient force magnetometer. The barium ferrite nanoparticles exhibit ferromagnetic behaviour at room temperature, with a saturation magnetization of 53 emu/g and a coercivity of 2430 Oe. Distribution of the BaFe12O19 nanoparticles into the polymeric matrixes increases the coercivity dramatically.