The tribological properties of oil-soluble nickel octoxyborate were evaluated using four-ball and ringon-block rigs. The results indicate that the wear resistance and load-carrying capacity of 500SN base oil were increased and its friction coefficient was decreased by the additive. The surface analysis of XPS indicates that nickel oxide,diboron trioxide,FeB and Fe2B have been deposited on the rubbing surface. It was these depositions that provided the oil with excellent antiwear and friction-reducing properties.