The mode of corrosion inhibition of amorphous FeBSiC alloy due to 3-amino-1,2,4-triazole (ATA) in molar HCl is studied through weight loss and electrochemical steady-state and transient measurements. From the comparison of results with those obtained using other ’triazole’ type-organic compounds, it is shown that ATA is the best inhibitor. ATA acts on the cathodic reaction without changing the mechanism of the hydrogen evolution reaction. Impedance studies show that ATA acts by formation of a 3D compact and protective adsorbed inhibition film at the metal surface which is similar to a paint or polymer film. A correlation between the inhibition efficiency of ATA and its molecular structure is established. A schematic representation of surface coverage due to different adsorption modes of ATA is presented. The schematic representation proposed explains why the mechanism of hydrogen reduction is the same in the absence and in the presence of ATA.