Monodispersed spherical zinc aluminate spine] (ZnAl2O4) nanoparticles were synthesized via a solvothermal method and modified by oleic acid in cyclohexanol solution. The nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and infrared spectrum (IR). The dispersion ability of nanoparticles in lubricant oil was measured with optical absorbance spectrum. The results show that the modified nanoparticles are nearly monodispersed and can stably disperse in lubricant oil. The tribological properties of the ZnAl2O4 nanoparticles as an additive in lubricant oil were evaluated with four-ball test and thrust-ring test. For comparison, ZnO and Al2O3 nanoparticles as additive in lubricant oil were also tested respectively. The results show that ZnAl2O4 nanoparticles exhibit better tribology properties in terms of anti-wear and anti-friction than ZnO or Al2O3 nanoparticles. The anti-friction and anti-wear mechanisms were discussed and the lubricating effect of ZnAl2O4 nanoparticles can be attributed to nano-bearings effect and tribo-sintering mechanism. (C) 2012 Elsevier Ltd. All rights reserved.