PURPOSE: To decrease the burden for processing of waste water by using a tetrazole compd. expressed by formula or its water-soluble salt as an anti-corrosive agent for metals.

CONSTITUTION: In formula, R, R', are hydrogen atom, a 1-20C alkyl, cycloalkyl, phenyl alkyphenyl amino, mercapto, or alkylmercapto group. This tetrazole compd. or its water-soluble salt is used as a water-soluble cutting and grinding oil for iron, water-soluble cutting and grinding oil for sintered hard alloys, rust preventive for cooling water of internal combustion engine, water-soluble surface treating agent for iron, and water-soluble surface treating agent for copper. It is required that the compd. has at least 0.001% solubility in water at room temp., and preferably ≥0.01%. The obtd. agent has an excellent corrosion preventing effect for various metals and shows a stable effect at low concn.