Abstract: Novel water lubricating additive of polytetrafluoroethylene@silica (PTFE@SiO₂) core-shell composite particles with submicron size was prepared by in-situ polymerization. The core-shell structure, composition and size distribution of the composite particles were determined by scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared spectrum (FTIR) and particle size distribution, respectively. The water dispersion test indicated that the as-synthesized particles had good water dispersibility and stability. The tribological properties of the particles as water lubricating additive at different testing conditions was investigated by LSR-2M reciprocating friction and wear testing machine. The results illustrated that the PTFE@SiO₂ lubricant had the best water lubricating properties under the speed of 0.019 m/s and the steel surface roughness of 0.2 μm as well as the ambient temperature. The friction coefficient was decreased nearly by 80% and the wear volume was reduced by 1~2 order of magnitude when compared with the lubricants of pure water and water with physically mixed PTFE and SiO₂ (PTFE/SiO₂). SEM observation demonstrated that the existence of core-shell structure and the formation of high-quality transfer film during the friction all contributed to the excellent water lubrication performances of PTFE@SiO₂ lubricant, and then a possible lubrication mechanism on this basis was also proposed.