The electrospinning method has been employed to fabricate ultrafine nanofibers of high-performance polyarylene ether nitriles (PEN) and PEN/Fephthalocyanine/ Fe3O4 nanocomposite fibers for the first time. Through optimizing the operational conditions, such as polymer concentration, applied electric voltage, federate, and distance between needle tip and collector, bead-free and uniform fibers with smooth surfaces and certain diameters were obtained. The morphology of the PEN nanofibers is correlated to the corresponding rheological behaviors of the polymer solutions. The nanocomposite fibers showed a beads-in-string structures without agglomeration after introducing the Fe-phthalocyanine/Fe3O4 hybrid microspheres in the polymer fibers. Thermogravimetric analysis (TGA) and differential scanning calorime-try (DSC) reveal an enhanced thermal stability of the nanocomposite fibers after introducing the hybrids. The glass transition temperature (T-g) of the nanocomposite fibers increases by 10 degrees C with 30 wt % hybrid microspheres, compared with those of the pure PEN fibers. The magnetic properties of the PEN/Fe-phthalocyanine/Fe3O4 nanocomposite fibers are different from those of the hybrid microspheres. The hybrid microspheres in the composite nanofibers become magnetically harder with a much larger coercivity than that of the fillers. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1732-1739, 2012