Abstract: Nano-SiO2 particles were prepared by sol-gel method with tetraethyl-orthosilicate as raw material in the presence of ammonia as catalyst. The morphology and phase structure of nano-SiO2 particles were characterized by TEM. The tribological properties of colza oil lubricant which took nano-SiO2 particles as additive in different mass fractions were investigated on a four-ball friction/wear tester. The worn surface of the steel balls was observed by SEM and the surface element composition was determined by means of energy dispersion spectrometry. The results show that the nano-SiO2 particles are amorphousely spherical-shaped with single particle size about 50 nm, and they can provide high surface energy/activity, and make for the locked-in absorbing films. With the nano-SiO2 particles as additive, the PB and PD values of the colza oil lubricant increase significantly. The lubricating effect will be the best if the additive is 2.5 wt%, and in such a case the worn scar diameter is minimum.