Contact angle and scratch tests have been conducted to investigate the effects of nano-TiO2 additive in oil-in-water (O/W) lubricant. The results show that the contact angle between high-speed steel with oxide scale and 1% (oil concentration) O/W lubricant decreases first and then increases as the concentration of nano-TiO2 particle in the O/W lubricant increases. The smallest contact angle is obtained after an addition of 4% nano-TiO2 additive to the O/W lubricant. This is because the nano-TiO2 can enhance the surface excess of the oil when the nano-TiO2 particles distribute throughout the surface of the oil droplets, and after saturation they can distribute throughout the water and also improve the surface excess of the water in the O/W lubricant. The scratch and hot rolling tests show that the nano-TiO2 particles in the O/W lubricant can also reduce friction, improve scratch resistance, and reduce rolling force. A method for measuring the adhesion force of the oxide scale is proposed and the effect of nanoparticles is discussed. It is demonstrated that the effect of self-lubrication of nanoparticles in the O/W lubricant plays a more significant role in the tribological behavior during hot rolling than wettability.