Abstract: Bio-fuel soot (BS) was collected with a homemade soot trapping equipment. A four-ball friction and wear tester was used to investigate the effect of BS on the tribological performance of liquid paraffin (LP). The composition, structure and tribological mechanism of BS were investigated by means of scanning electron microscopy/energy-dispersive spectrometry, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and X-ray diffraction. Results show that chain-like agglomeration of BS was composed of spherical nanoparticles with an average size of about 40 nm. The main ingredients of BS included amorphous carbon and oxygen, as well as a small amount of graphene microcrystal, and the oxygen content of BS was higher than that of diesel soot. With increasing content of BS in LP, the maximum non-seizure load firstly increased and then decreased. In addtion, the average wear scar diameters rose linearly, and the average friction coefficient firstly decreased slightly and then increased. In terms of the tribological mechanism, on the one hand, owing to the action of O-containing functional groups, BS can be easily adsorbed on rubbing surface thereby influencing the effect of boundary lubrication film. On the other hand，BS caused abrasive wear and corrosive wear and promoted detachment of metal oxide film on rubbing surface as abrasive particles，and thereby enhanced wear of the steel-steel sliding pair.