Sinapinic acid was studied for possible use as an Al-2.5Mg alloy corrosion inhibitor in a 0.5 mol dm(-3) NaCl solution. Measurements were performed on a rotating disc electrode in a quiescent solution and at different electrode rotation rates and electrolyte temperatures. Electrochemical parameters for the Al-2.5Mg alloy were determined using polarization techniques and electrochemical impedance spectroscopy (EIS). The investigated compound acts as a cathodic-type inhibitor and the inhibition is ascribed to the adsorption of the inhibitor onto the electrode surface. The electrode coverage follows the Freundlich adsorption isotherm.