The adsorption behaviour of triethanolamine (TEA) on aluminium, AlMgSi and AlZnMg alloys covered with naturally formed oxide films was investigated in 0.5 m NaCl solution, pH 1.3, by means of potentiodynamic and electrochemical impedance spectroscopy techniques. The results of polarization measurements show that in all cases the addition of TEA induces a decrease in the cathodic currents without affecting the anodic polarization behaviour, and, accordingly, TEA can be treated as a cathodic type inhibitor. The adsorption behaviour of TEA on the electrode surface follows a Frumkin isotherm with constants : a = 1.74, B = 18.41 dm3 mol-1. The results of impedance measurements presented in Nyquist plots show a high frequency capacitive loop related to the dielectric properties of the oxide film and a low-frequency inductive part which was determined by the faradaic process and attributed to the localized corrosion.