In order to study the effect of the unsaturated components in biodiesel oils on diesel oils,different percentages of unsaturated fatty acid methyl ester,stearic acid methyl ester were added into diesel oils respectively,and the effect of unsaturated fatty acid methyl ester on tribological behaviors of diesel oils was evaluated on a fourball wear tester.The corresponding topographies of worn surfaces tested with different diesel oils were analyzed by optical microscopy.The results indicate that the unsaturated fatty acid methyl ester can improve the tribological behaviors of diesel oils to some extent.Moreover,along with increasing of the unsaturated fatty acid methyl ester content,the friction reducing and antiwear performance of the diesel oils is shown the tendency of increasing gradually.The tribological behavior of the diesel oils added with unsaturated fatty acid methyl ester and stearic acid methyl ester is lowered after oxidation,especially the diesel oil with unsaturated fatty acid methyl ester has a more obvious decreasing in tribological behavior after oxidation.