Abstract: Disclosed is an additive for aqueous lubricants which can provide aqueous lubricants excellent in bacteriocidal action, rust proofness, emulsifiability and dissolvability and show no deterioration during use. This additive contains a piperazine compound represented by the general formula [I] or a reaction product of said piperazine compound with a carboxylic acid of 2-55 carbon atoms: ##STR1## wherein R.sup.1 -R.sup.8 represent hydrogen atom or alkyl group of 1-18 carbon atoms and m is an integer of 1-5. This additive may further contain an emulsifier or a lubricating oil.