PURPOSE: To enhance the corrosion inhibiting effect and safety of a water soluble corrosion inhibitor and to prevent foaming by using a pyroglutamate as the effective component.

CONSTITUTION: This water soluble corrosion inhibitor contains one or more kinds of compounds selected among the alkali metallic salts, ammonium salt and alkanolamine salts of pyroglutamic acid such as sodium pyroglutamate as the effective component. The corrosion inhibitor is generally effective when used by ≥ about 0.1%. The corrosion inhibitor has high safety and does not foam up because it has no surface activating power. The corrosion inhibitor does not produce scale or scum even when added to highly hard water, and it is applicable to iron, copper, Al, Zn and alloys thereof in natural water, tapwater, industrial water, seawater, cooling water or the like.