Hydrophobic nanoparticles were assembled into large-area monolayer films by combining oil/water interfacial self-assembly and phase separation of mixed ligands. Mixed ligands-capped nanoparticles were prepared simply by partially replacing the initial ligands of nanoparticle surfaces with polyvinylpyrrolidone (PVP). Infrared spectra and X-ray photoelectron spectroscopy demonstrate that O atom of PVP binds to the nanoparticle surface, changing the wettability of the nanoparticle. By controlling the polarity of solvent, nanoparticles can spontaneously migrate to toluene/water interfaces, forming large-area, close-packed monolayer films. This approach provides a straightforward way to fabricate nanoparticle films with a centimeter-scale size without LB trough, and may have potential applications in the fabrication of catalytic electrodes and photovoltaic electrodes. (C) 2013 Elsevier Inc. All rights reserved.