Cu-Ni bimetallic nanoparticles surface-capped with dodecanethiol were prepared via the controlled reduction of nickel nitrate and copper nitrate in the presence of dodecanethiol as ligand and hydrazine hydrate as reductant. The morphology and structure of the Cu-Ni nanoparticles were analyzed by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry, and thermal gravimetric analysis. Furthermore, the tribological properties of the Cu-Ni nanoparticles as a lubricant additive in liquid paraffin were evaluated with a four-ball machine, and the morphology and elemental composition of the worn surfaces were analyzed by three-dimensional non-contact surface profilometry and X-ray photoelectron spectroscopy, respectively. The results indicated that Cu-Ni nanoparticles prepared at a sufficient dodecanethiol concentration showed almost no signs of aggregation, and exhibited good dispersibility in various apolar solvents. The addition of the Cu-Ni nanoparticles improved the load-carrying capacity as well as friction-reducing and anti-wear abilities of liquid paraffin, attributed to the rolling effect of agglomerated Cu-Ni nanocores released by the Cu-Ni nanoparticles during sliding, and the formation of a boundary lubricating film containing tribochemical reaction products such as iron oxides and iron sulfate.