The chemical composition of the aqueous-alcoholic extract of fenugreek seeds and its influence on the corrosion resistance of carbon steels were determined. To assess the anti-corrosion properties of the extract, gravimetric and electrochemical methods of studying polarization resistance were used. The optimal concentration of the aqueous-alcoholic extract of fenugreek seeds in a 0.1M HCl solution was established - 40 g/l, the degree of protection - 91.39%. The presence of an after-effect effect after treating the steel surface with a disinfecting acid solution with the addition of the extract was revealed. To explain the mechanism of the protective effect, the composition of volatile organic compounds of the fenugreek extract was identified using chromatography-mass spectrometry. It was defined that the composition of the aqueous-ethanol extract of fenugreek seeds includes: alcohols (5.5%), aldehydes (40.1%), ketones (4.24%), methyl eugenol (7.7%) and terpenes (16.4%) - 1,8-cineole, dihydrocitronellol, Сarvone, Сarvacrol, p-cymene, Limonene, γ-terpinene. The electronic charges on the reaction centers of the active components were calculated. The negative electron density is most concentrated on the Oxygens of the carbonyl and hydroxyl groups of terpene-like aldehydes and alcohols, which ensure the formation of a protective layer on the steel surface.