Abstract: The effect of some sulfuretted fats as additives on the tribochemical properties of rape-seed oil was investigated on a four-ball friction wear tester with refined rape-seed oil taken as base oil. It was found that these fats can improve the load-carrying capacity and antiwear antifriction ability of rape-seed oil, with the wear spot diameters reduced if the small amount of additive increases to a certain extent. The wear spot diameters increase if increasing further the additive amount. The pB and the PD values also increase with the increase of additive amount. In particular the effect of additive RC2540 on sinter charge is so obviously that adding 3% RC2540 enable the pD value to up to 7845 N. The results of SEM and SEDX analysis show that the sulfuretted fats can cause tribochemical reactions in the friction process to form an extreme pressure protection film containing active sulfur element, which plays the role of antiwear and antifriction.