The methanol extract of Chamaerops humilis L. leaves (MECHLL) obtained by the soxhlet technique was analyzed by GC/MS and FT-IR spectroscopy. The extract is constituted by Lucenin 2 (42%), Dasycarpidan-1-methanol, acetate (ester) (11%), 1, 3-D-5-hexan-2-one-2, 4-dinitrophenylhydrazone (10%) and 9-Hexadecenoic acid (8%) as the most abundant compounds. The effect of the extract on the protective property of the oxide film formed on the reinforcement steel surface in alkaline solution (pH > 13) was investigated by electrochemical techniques. Inhibition efficiency of 42% was obtained with 0,5g/L of inhibitor at 25°C.The Nyquist plots showed that the variation of immersion time increases the polarization resistance and associated capacitance. The addition of the inhibitor can effectively decrease the reinforcement steel corrosion, enhance the stability of the film formed in alkaline solution and lead to the formation of a more compact protective layer on the surface. Action of the MECHLL obeys to the Langmuir adsorption isotherm. Finally the inhibition efficiency of the extract was discussed in terms of adsorption and protective film formation