Abstract: Oil soluble sodium alkoxyborate was synthesized and characterized with IR and ICP. Its tribological properties as friction reducing and anti wear additives of lubricating oil were evaluated with a four ball and block on ring tribotester. The morphology of the worn steel ball surface was observed and examined by means of scanning electron microscopy and X ray photoelectron spectroscopy. As the results, the additive could form a thick anti wear film on the rubbing steel surfaces and thus markedly improve the tribological properties of 500SN base oil. Deposition and tribochemical reaction of the lubricant were involved in the lubricated sliding of steel against steel, with the formation of FeB and Fe 2B on the rubbed steel surface. This contributes to improve the tribological properties of the base oil.