Molecular dynamics simulations have been performed to study the influence of methanol on the self-assembly of nanoparticles at liquid-liquid interfaces. The simulation shows that the methanol molecules, at low volume fraction, stay in the aqueous phase but with a preference of the water-trichloroethylene (TCE) interfaces. However, at higher methanol volume fraction, methanol dominates the aqueous phase and no preferable location of methanol molecules is observed. The simulations also suggest that the interfacial tension decreases and the interfacial thickness increases with increasing methanol concentration. The presence of the nanoparticles at water-TCE interfaces has minor effect on the interfacial properties compared to those of methanol, and the presence of methanol drives the noncharged nanoparticle clusters closer to the interfaces. Although the methanol molecules do not affect the monolayer distribution of the negatively charged nanoparticles at the water-TCE interfaces, they increase the three-phase contact angles of these nanoparticles.