Thiosemicarbazons show the ability to formation variegated of composition, constitution and properties of coordination compounds with metals, contain hydrazine NHgroups and atom of sulphur, as well as thiosemicarbazide, there was a hope that in the course of corrosion unsolvable complexes of iron and iron disulphide can be formed, capable to be switched on in covering layers and to enhance their antirust properties. During the conducted researches we have studied by electrochemical and physical methods (Uf - and Ik - spectroscopy, X-ray analysis and an electronic microscopy) agency of thiosemicarbazon of pyruvic acid on process of corrosion of steel St. 3 in water. With augmentation of concentration of inhibitor the solution is acidifying, in connection this, time before appearance of the first center of attack decreases. After 72 hours of tests on a corroding surface the continuous film of products of the corrosion remaining on a surface is formed. Their composition includes cubic oxide γ-Fe2O3, small amount an oxide α-Fe2O3, lepidocrocite γ-FeOOH and akagenite β-Fe2O3. Traces of calcite CaCO3 are found and the lines corresponding marcasite FeS2 are fixed, however in smaller quantity, than at thiosemicarbazide use. In the process of corrosion there is a gas emission - NH3 и H2S. With time in a protecting film products of interaction of the ionized iron with inhibitor and components of its decomposing collect and at 240 o'clock exposures the film completely consists of insoluble complex Fe(II) with thiosemicarbazon of pyruvic acid. It is confirming of Ik-spectroscopy of a scrape from a surface of the sample and its chemical analysis. It is positioned that repressing of a corrosion process in case of addition of the thiosemicarbazon of pyruvic acid more essential, than at use in qualities of inhibitor of thiosemicarbazide at all durations of tests, and repressing in time goes more resistant. So, for example, the minimum drag coefficient in case of an additive 0,1 g/l thiosemicarbazide and duration of tests of 8 hours accounts for 2,21 (at protection degree of only 54,7 %), whereas in case of an additive of thiosemicarbazon of pyruvic acid these indexes almost twice above - 4,0 and 75,1 % accordingly. The maximum repressing of corrosion is injected of thiosemicarbazon of pyruvic acid is observed at concentration 0,25 g/l and duration of tests 24 hours: the drag coefficient is equal 6,9, protection degree compounds 85,3 % whereas at addition of thiosemicarbazide they are accordingly equal 4,93 and 79,7 % at concentration of inhibitor 0,5 g/l and the same duration of exposure. Thus, presence of a thiosemicarbazon of pyruvic acid at water with difficulty influences process of corrosion of steel. The augmentation of concentration of an additive leads to increase of acidity of solution and reduction of time before appearance of corrosion centers during the initial moment of tests that together with shift of potential in a negative side testifies to augmentation of speed of anodic process. In the subsequent the potential is stabilized at the expense of interaction of ions Fe(II) with inhibitor and formations on a surface of a steel of an almost insoluble complex of bivalent iron with inhibitor. With formation of film the diffusion of oxygen to a surface is impeding therefore polarization of its cathodic restoration is increasing, and metal ionization is retarding. In the process of corrosion there is also an inhibitor decomposing on fragments, gassing NH3 and H2S, interaction of the last with ions of iron that leads to formation of marcasite, also joining in an integumentary film and inhibiting corrosion process