Abstract: A corrosion-inhibiting method for protecting steel materials in concrete or mortar, characterized in that a nitrite, a compound of general formula NH(R)CH.sub.2 COOH (wherein R represents a H atom or an alkyl group having 1 to 4 carbon atoms) or salts thereof, and a hydrazine hydrate are incorporated into the concrete or mortar is provided. The corrosion-inhibiting method is particularly available for construction of steel reinforced concrete structures in which chloride-containing sea sand is used as aggregates and does not affect a property of the concrete or mortar.