Abstract: TiO 2 nanoparticles surface modified with cis 9 octadecenoic acid (OA) with average diameter of 50 nm was chemically synthesized by sol gel method. The resulting surface modified nanoparticles were characterized by means of infrared spectrometry and transmittance electron microscopy. They were also dispersed in water in the presence of tea saponins as surfactant, so as to obtain an O/W emulsified liquid. The tribological and cutting properties of the composite emulsified liquid were evaluated with a four ball tester and a metal cutting fluid tapping torque evaluation tester. The results show that the emulsified liquid exhibits good tribological behavior and cutting performance. The maximum non seizure load ( p B value) of the fluid is as high as 804 N, while the welding load ( p D value) and tapping torque are considerably increased at proper concentrations of the tea saponins (>2.5%).