Abstract: Monodisperse ZrO2 nanoparticles were prepared in trioctylphosphine oxide (TOPO) and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transformation infrared spectroscopy (FTIR). The results showed that the as-prepared nanoparticles were 7~8 nm in diameter, rarely aggregated, and can easily dissolve and stably disperse in apolar organic solvents. The tribological properties and lubrication mechanism of ZrO2 nanoparticles as MACs additive were investigated. X-ray photoelectron spectroscope (XPS) and scanning electron microscopy (SEM) results indicated that the synergistic action of both ZrO2 ceramic film and FePO4 lubricant film formed in the rubbing process markedly improved the load-carrying capacity and reduced the wear volume.