PURPOSE: To obtain a lubricant improved in abrasion resistance, oxidation deterioration resistance and metal corrosion by adding a sulfur-containing heat- resistant abrasive agent or an extreme pressure agent and two kinds of specific amine salts to a polyalkylene glycol having lubricating viscosity.

CONSTITUTION: A lubricant compsn. consists of a major proportion of a polyalkylene glycol of lubricating viscosity and a minor proportion dissolved therein of (a) at least one sulfur-containing antiwear or extreme pressure agent, (b) at least one amine salt of at least one partially esterified monothiophosphoric acid and (c) at least one amine salt of at least one partially esterified monothiophosphoric acid. Pref. amine in the above mentioned component (b) is aliphatic primary monoamine and, especially, one containing 6-100 carbon atoms in an alkyl, alkenyl or polyethylenic unsaturated aliphatic group. The component (c) is an amine salt of a partial ester of an orthophosphoric acid.