This paper deals with the influences of 2-ethylhexanol (residual alcohol in zinc dialkyldithiophosphate) on the antioxidation, anti-friction and anti-wear of zinc dialkyldithiophosphate that is one of the additives widely used in engine lubricating oil. The results show that the 2-ethyihexanol results in the thermal degradation of zinc dialkyldithiophosphate earlier and decrements of the anti-oxidation and antifriction capacites of zinc dialkyldithiophosphate. The 2-ethylhexanol increases greatly the anti-wear property of zinc dialkyldithiophosphate.