Effectiveness of 2-methylpiperazinedithiocarbamato(2-Mepipzdtc) complexes of Cu(II) and Zn(II), diethyldithiophosphato (Et(2)dtp) complex of Ni(II) and its gamma-picoline diadduct, and pyrrolidine dithiocarbamato complex of Cu(II) are evaluated as antioxidant lubricating oil additives by measurement of viscosity, acid number, IR spectral and thermal studies. All the complexes at 0.25 and 0.5 wt% show antioxidant property. Zn(2-Mepipzdtc)(2) as well as Ni(Et(2)dtP)(2)(gamma-Pic)(2) were found to be most effective antioxidants among these compounds. The antioxidant behaviour has been explained on the basis of hydroperoxide decomposition and radical scavenger mechanism.