Magnetic NPs have been receiving increased attention with the rapid development of nanotechnology.Among them, Fe3O4 NPs have caused widespread interest owing to their high superparamagnetism as well as facile preparation. Their easy oxidation and resulting decline in magnetic property is a problem, however, which is effectively solved by the dispersion of Fe3O4 NPs in polymer nanofibers. The simplest way to prepare polymer/Fe3O4 composite nanofibers is to disperse Fe3O4 NPs in the polymer solution and subsequently carry out the electrospinning process. Xin et al. successfully fabricated poly(p-phenylene vinylene)/Fe3O4 composite nanofibers via electrospinning of a precursor solution and subsequent thermal conversion (Fig. 3.14A). In addition, the aligned nanofibers can be obtained by employing two parallel magnets as the collector (Xin et al., 2009). A variety of polymer/ Fe3O4 composite nanofibers, including PAN/Fe3O4 composite nanofibers (Zhang et al., 2009a; Wang et al., 2010a), gelatin/Fe3O4 composite nanofibers (Wang et al., 2014c), etc., have been reported by means of a similar method, and their potential applications in various fields have been studied as well (Zhang et al., 2017; Wang et al., 2004; Kumar et al., 2007; Venugopal et al., 2014; Chiscan et al., 2012a; Zheng et al., 2017). Moreover, considering that Fe3O4 NPs are always synthesized in aqueous solutions, the obtained Fe3O4 NPs can be easily transferred into organic solvents via surface modification. Wang et al. (2014a) utilized oleic acidecoated Fe3O4 and PLLA to prepare electrospun PLLA/Fe3O4 composite nanofibers. Some researchers have found that polymer/Fe3O4 composite nanofibers can be obtained without the use of Fe3O4 NPs directly. For instance, Tura et al. mixed FeCl3 and PVC in solvent, and successfully synthesized PVC/Fe3O4 composite nanofibers through electrospinning (Fig. 3.14B) (Tura and Mangalagiu, 2010). Luo et al. (2016) fabricated magnetic polyimide (PI)/Fe3O4 composite nanofibers by electrospinning a mixture of polyamide acid/ferric acetylacetonate in solution followed by a thermal process. Furthermore, the coaxial electrospinning technique as well as other novel routes has also been widely applied in the preparation of polymer/ Fe3O4 composite nanofibers (Yu et al., 2014; Ma et al., 2012b; Sharma et al., 2010; Jiang et al., 2015; Liu et al., 2015; Wang et al., 2010b).