Iron oxide nanoparticle coated poly(ethylene oxide) nanofibers as organic-inorganic hybrids with 200-400-nm diameters were prepared by the in situ synthesis of iron oxide nanoparticles on poly(ethylene oxide) nanofibers through the electrospinning of a poly(ethylene oxide) solution having Fe2+ and Fe3+ ions in a gaseous ammonia atmosphere. Transmission electron microscopy analysis proved the presence of iron oxide nanoparticles on the polymer nanofibers. The thermal properties of the nanofiber mat were also studied with differential scanning calorimetry and thermogravimetric analysis techniques. X-ray diffraction showed that the formed iron oxide nanoparticles were maghemite nanoparticles. The results were compared with those of the electrospinning of a poly(ethylene oxide) solution having Fe2+ and Fe3+ ions and a pure poly(ethylene oxide) solution in an air atmosphere. (c) 2007 Wiley Periodicals, Inc.