An alternative strategy, adopting the magnetic composite nanoparticles in the hole injection layer, is proposed in this Letter to obtain efficient organic light-emitting devices (OLEDs) by simultaneously integrating the localized surface plasmon (LSP), light-scattering, and magnetic field effects (MFE). A 90% increase in the current efficiency of Alq-based fluorescent OLEDs is obtained by using the FeO@Au nanoparticles (FOA NPs), compared with the device without NPs, arising from the LSP effect induced by Au NPs and the strong light-scattering effect related to FOA NPs. Meanwhile, the current efficiency can be further increased by ∼20% under an external magnetic field (EMF) of 0.5 T due to the increased singlet exciton induced by the spin injected holes via FOA NPs. Moreover, with an EMF, the current efficiency of Ir(ppy)(acac)-based OLEDs is decreased slightly, implying that the emitting material system and mechanism have a great effect on the MFE. These results confirm the extensive use of FOA NPs in OLEDs and pave a new way to construct the FOA-NPs-based white OLEDs with both fluorescence and phosphorescence emitters, whose intensity and color can be modulated.