A bismuth diamyl-dithiocarbamate additive was synthesized. A four-ball tester was used to evaluate the tribological performance of the additive in mineral oil, and compared with same types of metal additives. The results show that it exhibits better load-carrying capacities than said organic metal additives. The surface analytical tools such as X-ray photoelectron spectrometer (XPS) and Scanning electron microscopy (SEM) were used to investigate the topography, the compositions contents and the depth profile of some typical elements on the rubbing surface of worn scar. Smooth topography of worn scar further confirms that the additive showed good antiwear capacities, the results of X-ray photoelectron spectrometer and X-Ray Energy Dispersive Spectroscopy analyses indicated that tribochemical mixed protective films consists of bismuth compounds, sulfides, sulphates were formed on the rubbing surface, which contribute to improve the tribological properties of lubricants. Particularly, a large amounts of bismuth atoms play an important role in improving antiwear properties of oils.