This work presents the results concerning the effect of different concentrations of an organic heterocyclic compound that displays corrosion inhibiting properties, known as 2-mercaptobenzimidazole, 2MBI, in a system comprising samples of the steel type API 5L X52 exposed to HCl 1M. The impedance spectra revealed that there was a continuous increase of |Z| as a function of increasing inhibitor concentrations in the electrolyte. A 200 ppm 2MBI was tested also, however, the greatest corrosion inhibiting efficiency was attained 99%, IE, with much smaller concentrations of the compound. This is sufficient reason to consider it a good corrosion inhibitor in HCl, just as it was effective for H 2 SO 4 . Furthermore, the inhibition kinetics study undertaken indicated that the 2MBI added in a fairly large concentration of 200 ppm in 1M HCl maintains its effectivity up to 32 immersion days. Also, it was observed that the corrosion potential, E corr , became more negative as the 2MBI organic molecules concentration increased in the system, which suggests that this inhibitor may be acting on the cathodic and anodic sites, thus being considered a mixed type inhibitor, in agreement with the corrosion mixed potential theory