Among various types of nanomaterials, nanofibers have attracted much attention because of their intriguing chemical and physical properties.[1] The most widely used method for nanofiber preparation is template synthesis. This method involves the introduction of organic, inorganic, and metallic materials within channels of templates, such as silica, [2] anodic aluminum oxide, [3] zeolites, [4] and track-etched polycarbonates.[5] To date, microemulsion polymerization has been considered to be a facile process to produce polymer nanomaterials as reviewed by Antonietti and co-workers.[6] While nanoparticles, [7] hollow nanospheres, [8] and nanotubes [9] of several polymers were fabricated by using microemulsion polymerization, the synthesis of polymer nanofibers has not yet been performed. Herein, we report that novel polyacrylonitrile (PAN) nanofibers and carbon nanofibers with a high aspect ratio were fabricated by using a salt-assisted microemulsion polymerization. In this work, iron(iii) chloride (FeCl 3 ) was employed as a structure-directing agent, it forms a coordination-complex with PAN nanoparticles during polymer nanofiber formation, and it acts as a catalyst for the conversion of the polymer into the carbon nanofibers. Salt-assisted sphere-to-cylinder micelle transformation is the crucial step for nanofiber formation. To the best of our knowledge, this is the first experimental evidence for the fabrication of carbon nanofibers derived from polymer nanofibers by using a salt-assisted microemulsion polymerization.The overall fabrication procedure is presented in Figure 1. In a typical procedure, a variable amount of dodecyltrimethylammonium bromide (DoTAB) was magnetically stirred in 40 mL of distilled water at room temperature. Monomeric acrylonitrile (AN) was added dropwise to the micelle solution and monomers inside micelles were polymerized by using redox initiators, cerium sulfate and nitrilotriacetic acid (NTA). After 30 min of polymerization, iron(iii) chloride was introduced and the polymerization proceeded for an additional 4 h with magnetic stirring. The product was precipitated in methanol to remove surfactants and initiators.When surfactants are dissolved in water, spherical micelles form between CMC (CMC = critical micelle concentration, 0.016 m for DoTAB) and the concentration of transformation of sphere to cylinder (0.32 m for DoTAB). [10] After 30 min of polymerization, the size of PAN nanoparticles were approximately 20 nm (Figure 2 a). It was reported that Figure 1. The overall fabrication scheme for PAN nanofibers by using a salt-assisted microemulsion polymerization. Figure 2. a) TEM image of fabricated PAN nanoparticles. A surfactant, DoTAB was used for micelle formation and acrylonitrile monomer (1 g, 0.02 mol) was polymerized with initiators, cerium sulfate, and nitrilotriacetic acid; b) SEM image of fabricated PAN nanofibers. PAN nanofibers were obtained by addition of iron(iii) chloride (1.0 g, 6.2 mmol) in the middle of polymerization reaction. The inset shows the TEM image of t...