Abstract: Magnesium borate nanoparticles modified by oleic acid triethanolamine were successfully synthesized by direct deposition and was characterized by means of transmission electron microscopy,X ray diffraction and infrared spectroscopy respectively.The effect of nanometer magnesium borate used as additives in aqueous solution on the lubricating behavior was investigated using a four-ball tester.The nanometer magnesium borate.The worn surfaces of the stee1 ball were analyzed by scanning electron microscopy.It was found that the average size of magnesium borate nanoparticles was 40～60 nm,and the surface of magnesium borate nanoparticles reacted with surface modifier via chemical adsorption.The results indicated that a layer of lubricating membrane was formed between the surfaces of the friction pairs.XPS analysis of the wear scar showed that MgO,B2O3,FeO and Fe2O were formed on the rubbing surface which provided the aqueous solution with good lubricating properties.