Abstract: CoFe2O4magnetic nanoparticles were dealt with nitric acid to forman ionization surface and to improve the dispersibility of CoFe2O4 nanoparticles greatly. Then polyaniline (PANI)/CoFe2O4 electromagnetic nanocomposites with different amounts of CoFe2O4 were synthesized by in-situ polymerization method. The morphologies, structures, and electromagnetic properties of the PANI/CoFe2O4 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR) spectra, four-probe electrometer, and vibrating sample magnetometer (VSM). The results indicated that the CoFe2O4 magnetic nanoparticles with diameter of about 25 nm were dispersed in the base of PANI and the bonding interaction existed between CoFe2O4 particles and polyaniline in the composites. The composites possessed both conductivity and magnetism. With increasing CoFe2O4 content, the conductivity of the composites decreased while the saturated magnetization (Ms) increased. Increasing CoFe2O4 content from 16.8%to 69.2%, the coercive force (Hc) of PANI/CoFe2O4 nanocomposites was higher than that of the CoFe2O4 nanoparticles and increased firstly and then decreased.