The inhibition effect of cetyl trimethyl ammonium bromide (CTAB) as a cationic surfactant on the corrosion of carbon steel in different HCl concentrations has been studied at different temperatures by weight loss, open circuit potential, Tafel polarization and linear polarization methods. The results show that CTAB is a good inhibitor in 2M HCl, and the inhibition efficiency (IE) increases with the inhibitor concentration, while it decreases with increasing the hydrochloric acid concentration more than 2M and temperature. Effect of immersion time was also studied and discussed. The adsorption of inhibitor on the C-steel surface obeys the Langmuir adsorption isotherm equation. Polarization curves show that CTAB is a mixed-type inhibitor in hydrochloric acid. The results obtained from weight loss and polarizations are in good agreement.