A new magnetic–fluorescent bifunctional coaxial nanobelt structure has been successfully fabricated by specially designed coaxial-spinneret electrospinning technology. As an example, terbium complexes [Tb(BA)3(phen)] (BA=benzoic acid, phen=1,10-phenanthroline) and ferroferric oxide nanoparticles were incorporated into polymethyl methacrylate (PMMA) and electrospun into coaxial nanobelts with Fe3O4/PMMA as the core and [Tb(BA)3(phen)]/PMMA as the shell. The morphology and properties of the final products have been investigated in detail by X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), biological microscopy (BM), vibrating sample magnetometry (VSM), and fluorescence spectroscopy. The results show that the [Fe3O4/PMMA]@[[Tb(BA)3(phen)]/PMMA] magnetic–fluorescent bifunctional coaxial nanobelts possess superior magnetic and fluorescent properties owing to their special nanostructures. The magnetic–fluorescent bifunctional coaxial nanobelts provide higher performance than Fe3O4/[Tb(BA)3(phen)]/PMMA composite nanobelts. This new type of magnetic–fluorescent bifunctional coaxial nanobelt has the potential to be used in novel nano-biolabel materials, drug delivery materials, and future nanodevices owing to their excellent magnetic–fluorescent properties, flexibility, and insolubility.