Oleic acid modified CuS and Mn2+-doped CuS nanoparticles were prepared respectively.TEM study shows that the particle size of obtained samples is about 10 nm,and the samples have good oil dispersibility and stability.As additives of lubricating oils,the nanoparticles were added into liquid paraffin,the friction and wear properties were investigated.The results show that oleic acid modified nanoparticles have excellent antiwear and load-carrying capacity.Compared with normal liquid paraffin,when lubricated by liquid paraffin containing 0.1%(mass fraction) oleic acid modified Mn2+-doped CuS nanoparticles,the wear scar diameter is reduced by 30%,the maximum load-carrying capacity is increased by 40%.The morphologies of worn surfaces were observed by SEM,the results show that the friction trace when lubricated by the liquid paraffin containing Mn2+-doped CuS nanoparticles is shallower than that when lubricated by the liquid paraffin containing undoped CuS nanaoparticles.