Polyaniline/Fe3O4 nanocomposite was synthesized via micro-emulsion polymerization of aniline in the presence of Fe3O4 nanoparticles. The experimental results revealed that a core-shell structure composite was obtained successfully. Electrospinning of Fe3O4-polyaniline/polyacrylonitrile (Fe3O4-PANI/PAN) blended with different composition ratios were performed using N,N-Dimethylformamide as solvent. Morphology and fiber diameters were investigated by means of scanning electron microscopy. Electrospun fibers with diameters ranging from 168 to 300 nm were obtained. Scanning electron microscopy images indicated that the diameter of the composite nanofiber increases with the content of Fe3O4. It was also found that the permittivity was decreased by the addition of Fe3O4, but the permittivity was increased relevantly if the Fe3O4 mass fraction in the Fe3O4/PANI was increased. The thermal stability of the composite nanofibers is also examined in this paper.