Oil-in-water (O/W) based nanolubricants have the potential to improve the stability of O/W emulsion system and reduce friction, thereby enhancing the efficiency of the lubrication. In this paper, the stability, dispersibility and tribological properties of O/W based nanolubricants with varying mass fractions of oil and TiO2 nanoparticles were investigated. The results show that nanolubricants have good dispersibility and stability. The coefficient of friction (COF) is reduced by 16.3% with the addition of 2.0% TiO2 nanoparticles to the O/W lubricant (1.0% oil). The lubrication mechanism of the O/W based nanolubricants with addition of TiO2 nanoparticles is proposed. The nanoparticles existing in the oil pool can enter the contact area to significantly reduce the COF and increase the weight loss. Increased COF will be induced due to aggregation of nanoparticles around the oil pool.