A great challenge on tribology is the improvement of vegetable oils lubrication properties, which are environmentally friendly products, to replace long established lubricants based on mineral oils (petroleum). It is well known that some traditional additives used with mineral oils, such as organic sulfides, present antagonistic effects on vegetal oils on anti-wear boundary lubrication property. This work used natural rapeseed oil and sunflower oil to study the influence of the organic sulfides and the trans-fatty acids on the natural triglycerides. The tests used were a reciprocating motion test (SRV) and a unidirectional motion test (four ball test). The results show the same trend: the presence of trans isomers in the lubricant in combination with certain additives may significantly influence their boundary lubrication properties. As it is expected, octadecanethiol additive decrease the anti-wear performance although in combination with trans acid at low temperature keep the neat conditions and at high temperature the anti-wear properties are enhanced.