To develop a potential substitute for conventional lubricant additive, pure calcium borate nanoparticles (PCBN) and calcium borate nanoparticles modified with oleic acid (MCBN) were prepared. The microstructures of the as-obtained samples were characterized using X-ray power diffraction (XRD), transmission electron microscope (TEM) and infrared spectra (IR), and the dispersing stability of oil containing nanoparticles was also evaluated. Tribological properties of MCBN used as lubricating additive were evaluated using four-ball tribometer and compared with that of PCBN. The results indicate that MCBN show better antiwear and friction-reducing property than PCBN. The worn surface of the steel ball lubricated with MCBN was investigated by Polarized microscope (PM) and X-ray photoelectron spectroscopy (XPS), and the action mechanism of MCBN during friction process was preliminarily discussed.