The Fe3O4 nanofibers were prepared by electrospinning method. The phase composition and morphology were analyzed by XRD and FE-SEM. The results indicated that the pure Fe3O4 nanofibers were obtained and exhibited evident shape anisotropy. The magnetic study via VSM showed that the Fe3O4 nanofibers possessed ferrimagnetic properties. The saturation magnetization was around 58.4 emu/g and the coercivity was approximate 186.7 Oe. In addition, the electromagnetic loss properties were detailed investigated by network analyzer. The dispersion relaxation phenomenon was observed in the frequency range of 2–18 GHz. The dielectric loss was caused by the interface polarization and the magnetic loss was owing to the exchange resonance. The as-prepared Fe3O4 nanofibers showed excellent electromagnetic loss properties and could be potentially applied as the lightweight microwave absorption materials.