Corrosion inhibition mechanisms of anionic precipitation inhibitors for metals in oxygenated neutral solutions are discussed based on the hard and soft acids and bases principle(HSAB principle). For example, fluoride ion F-, phosphonate ion CH3C(OH)(PO32-)2, benzotriazolate ion C6H4N3-, octylthiopropionate ion C7H15S(CH2)2CO2- and 8-quinolinolate ion are effective inhibitors for corrosion of metals like Mg, Al, Fe, Cu and Zn in oxygenated neutral solutions by the formation of stable acid-base bonds. They form precipitates of salts, complexes, complex polymers or chelate compounds on the metal surfaces and inhibit metallic corrosion by coverage with the precipitates. The stability of precipitate formation is closely related to the HSAB principle.