Abstract: The tribological performance of the bio-oil was evaluated by MQ-800 four-ball tribometer. The surface analytical tool SEM and XPS were used to investigate the morphology and distribution of active elements on rubbed surface on steel balls. The variation of chemical compositions and thermal property of bio-oil before and after friction were studied by GC-MS and TGA, respectively. The experimental results showed that the extreme pressure of the bio-oil was up to 392 N. The frictional coefficient of bio-oil varies between 0.083 and 0.097 with the 196 N and 294 N pressure. There were many belt-like ploughs on the rubbed ball surface, and the binding energy peaks such as the organic with hydroxyl group or carboxyl group, inorganic including FeS and FeSO4 were also investigated. The contents of the aldehyde and acid varied after friction experiments. It was shown that the film composed of FeS, FeSO4 and organic compounds with -OH and -COOH groups on the rubbing surface was ascribed to the good lubricate performances of bio-oil.