This study is concerned with the use of Congo red as an inhibitor for low alloyed carbon steel, petroleum steel and boron steel at 60 C in 3.5% NaCl aqueous solution. Analysis was performed using the Tafel polarization measurements and electrochemical impedance spectroscopy. Congo red was observed to cover the surface by adsorbing upon it, and its inhibition efficiency depended on the concentration. The efficiency was the highest one in low-alloyed carbons steels, followed by petroleum and boron steels. The type of adsorption occurring on the metal surface was also determined.