In order to improve the friction reducing and anti-wear ability of nickel nanoparticles as lithium grease additives,nickel nanoparticles were modified by oleylamine(OA) to reduce polymerization.The effects of as-prepared OA-Ni nanoparticles on the tribological properties were tested by four-ball and TE77 reciprocating friction testing machines,and the mechanism of friction reducing and antiwear of OA-Ni nanoparticles in grease was discussed.The as-prepared OA-Ni nanoparticles are irregular discs with a particle size of about 100 nm,which have good dispersion in grease.OA-Ni nanoparticles can effectively improve the tribological properties of lithium grease,and the anti-wear and friction reducing properties are increased by 36.6% and 15%,respectively.The results of wear surface analysis show that during the friction process,OA-Ni nanoparticles can form a tribochemical film with metal oxides such as Fe2O3,Fe3O4,NiO and Ni2O3 on the friction surface,which improves the tribological properties of lithium grease.