Abstract: The tribological properties of benzothiazole derivatives as additives in rapeseed oil were investigated using a four ball machine. The morphologies and chemical features of the worn steel surfaces were observed and examined by means of X ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). As the results, the two benzotriazole derivatives as additives obviously increased the load carrying capacity, antiwear and friction reducing abilities of rapeseed oil. The XPS analytical results of typical elements on the worn steel surfaces indicated that a boundary lubricating film composed of triester of rapeseed oil, S containing organic compound and sulfate were formed on the worn steel surface, by way of chemisorption and/or tribochemical reaction. This contributed to improve the tribological properties of the rapeseed oil base stock.