Boron-based compounds can be widely used in tribological applications such as lubricants, anti-wear additives and in addition to this, these compounds, especially borates, are environment friendly, easily available and cheap materials. In particular, nanoparticles are used as additives or lubricants to prevent friction and wear on steels. Nano-sized lubricants with novel unique properties such as wear resistance, low friction coefficient and high load capacity can be used as tribological materials. In this study, different amounts of platelet ladder-like calcium hexaborate pentahydrate (CaB6O10 center dot 5H(2)O) nanoparticles were used as a lubricant additive to characterize the effect of CaB6O10 center dot 5H(2)O on tribological properties of AISI 52100 steel. Synthesized calcium hexaborate pentahydrate nanoparticles were dispersed with different concentrations (0.1%, 0.5% and 1.0% wt.) in commercial engine oil, and tribological tests were conducted using ball-on-disk geometry. The morphology of surface was studied using scanning electron microscopy (SEM). Coefficient of friction was decreased by about 26.6% with the contribution of 1.0% wt. of CaB6O10 center dot 5H(2)O into the commercial engine oil (SAE10W40).