To suppress a corrosion of carbon steel in aqueducts closed systems , various organic compounds were used. Some of them were natural carboxylic acids and their derivatives, e.g. sodium pyruvate (stable salt of pyruvic acid) and aminoguanizons of pyruvic and α-ketoglutaric acids in concentrations varying from 0.05 to 1.0 g/l. R – CH2 – C = N – NH – C = NH | | ; CH3 – C – COONa COOH NH2 || O (R = H - ; HOOC – CH2 - ) Corrosion tests with samples fully immersed into solution were carried out. Corrosion losses were gravimetrically recorded. The inhibitor effect was evaluated by the corrosion rate k [g/m2 per 24 hours], and corrosion inhibition coefficient γ, which indicates how many times the corrosion rate is reduced by the inhibitor’s presence. Influence of inhibitor concentration on the change in stationary potential, pH of the medium, and corrosion losses was studied during the time trials. X-ray diffraction, chemical analysis, and IR-spectroscopy methods were used to study on composition of the surface protective layers, while UV-spectroscopy was used to determine changes in properties of the corrosive environment. It was determined that inhibitor changes the rate of metal ionization due to formation of the complex compounds resulting from interactions of the ferric ions with inhibitors or products of their decomposition. Formation of insoluble complexes in protective coating layers on the corroding surface through the pores in oxide film of the corrosion hydroxide products results in significant enhancement of protective properties of those layers and improves the overall corrosion resistance of the metal. It was determined that fine tuning of the inhibitor composition within the concentration range varying from 0.05 to 1.0g/l, secures corrosion loss decreasing by 9 to 5 fold, depending on the duration of the time trails. In conclusion, we have developed rather effective and ecology-friendly inhibitor which allows significant reducing of the steel corrosion losses.