Y2O3:Eu3+ nanoparticles (NPs), polyaniline (PANI), and Fe3O4 NPs are incorporated into polymethyl methacrylate (PMMA) and electrospun into [Y2O3:Eu3+/PMMA]//[PANI/Fe3O4/PMMA] Janus nanobelts with Y2O3:Eu3+/PMMA as one half side and PANI/Fe3O4/PMMA as the other. The morphology and properties of the final products are investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM), energy-dispersive spectrometry (EDS), Hall effect measurements, fluorescence spectroscopy, vibrating sample magnetometry (VSM), and UV/Vis spectroscopy. The results reveal that the [Y2O3:Eu3+/PMMA]//[PANI/Fe3O4/PMMA] trifunctional Janus nanobelts possess excellent electrical conductivity, magnetism, and fluorescence owing to their special nanostructure. Fluorescence emission peaks of Eu3+ are observed in the Janus nanobelts. The electrical conductivity reaches the order of 10(-4)Scm(-1). The luminescent intensity, electrical conductivity, and saturation magnetization of the Janus nanobelts can be tuned by adjusting the respective amounts of Y2O3:Eu3+ NPs, PANI, and Fe3O4 NPs. The flexible luminescent-electrical-magnetic trifunctional Janus nanobelts have many potential applications. More importantly, this design concept and construct technology is of universal significance for the fabrication of other multifunctional nanostructures.