Abstract: Two types of phosphorous nitrogen incorporated rapeseed oil were synthesized and characterized by means of infrared spectrometry. Their tribological properties as additives in rapeseed oil and mineral oil were tested on four ball machine. The friction reducing behavior of the additives in rapeseed oil was examined on an MM 200 friction and wear tester. The morphologies of the worn steel surfaces were analyzed by means of scanning electron microscopy (SEM). As the results, the two types of modified rapeseed oil as additives can obviously increase the load carrying capacity, antiwear and friction reducing abilities of rapeseed oil. It was supposed that a high strength adsorption film and/or tribochemical reaction film on the rubbing steel surfaces accounts for the improved friction and wear behavior under the lubrication of rapeseed oil containing the additives. The molecules of the rapeseed oil base stock with a long carbon chain help to strengthen the adsorption of the additive molecules on the steel surface, which together with the high reaction activities of the P and N in the additive molecules shows a synergism to improve the friction reducing and antiwear behavior of the lubricant.