This study aims to investigate the effects of castor oil and biodiesel on the tribological performance of engine oil. Five mixed types of engine oils (B0, B5, B100, 5B-5% and 10B-5%) were used as the testing oils. Tribological performance of the test oil was evaluated under different temperature and duration by Cameron Plint TE77 reciprocating rig. SEM, EDS and AES/XPS were separately to characterize the morphology of worn surface and indentify the composition of the surface films. The results show that the anti-wear ability of the engine oil mixed with castor oil is better than that of the engine oil mixed with biodiesel oil. At room temperature, the anti-wear ability of engine oil is dominated by the physical adsorption capacity and hydrodynamic effects; while at high temperature, the anti-wear ability of engine oil is depend on the moment of decomposition of ZDDP additive and its chemical reaction rate.