The carbon steel electrodes were first treated by immersion in 0.1 M phenyl phosphonic acid (C 6 H 5 P(O)(OH) 2, PPA) solution during 24 or 72 hours, then they were transferred into the corrosion test solution representing interstice pore electrolyte polluted by seawater:sat. Ca(OH) 2 + 0.5M NaCl) to evaluate the protective effectiveness of the pre-treatment. The investigation was performed essentially by polarization curves and electrochemical impedance measurements with rotating disc electrode. Very high protective effect was observed with steel pre-treated during 72 hours with stationary electrode. From polarization and electrochemical impedance spectroscopy experiments, the protective efficiency was found to be in the 90-99% range for 72 hour pre-treatment. This protective property remains effective even one month immersion. EDS analysis showed the presence of the phosphorus on the steel surface, probably due to the presence of iron-PPA complex.