Abstract: Four chlorine-containing organic borates were synthesized.The tribological propertiesof these compounds as oil additives were evaluated using a four-ball machine and a ring-blocktester,and the results were compared with those of non-chlorine containing organic borates andcetyl chloride,X-ray photoelectron spectroscopy(XPS)as used to examine the rubbed surfaces.It was found that the chlorine-containing organic borates are much effective in friction andwear mitigation and in increasing load-carrying capacity on four-ball tests,and they are also betterthan cetyl chloride and non-chlorine-containing borates on four-ball tests. Ring-block tests shownthat the chlorine-containing borates are as effective as but not superior to those of non-chlorine-containing borates in friction and wear reduction and in increasing of load-carrying capacity,andthey do have better friction reduction and antiwear properties than cetyl chloride. XPS analysesshown that the borates adsorb on the rubbed surfaces in the form of degradated borates,whilechlorine is mainly in the form of iron chlorides and chlorine-containing borate.