Abstract: Oleate/PS/TiO 2 composite nanospheres were prepared by means of seed polymerization. The effect of oleate/PS/TiO 2 nanospheres as additives on the antiwear ability and load carrying capacity of liquid paraffin was investigated on a four ball machine. The composition and chemical states of the elements on the worn steel surface were examined by means of X ray photoelectron spectroscopy. The results indicate that oleate/PS/TiO 2 composite nanospheres as additive can increase the antiwear ability and load carrying capacity of the base stock considerably. This is attributed to the formation of a chemical reaction boundary film consisting of TiO 2, Fe 2O 3 and organic compound.