Gentisic acid was studied for possible use as an Al-2.5Mg alloy corrosion inhibitor in a 0.5 mol dm(-3) NaCl solution. Investigations were performed on a rotating disc electrode in a quiescent solution at different electrode rotation rates and electrolyte temperatures. The results indicate that, the addition of gentisic acid inhibits corrosion of Al-2.5Mg alloy, and the inhibition efficiency increases with increasing inhibitor concentration but decreases with increasing electrode rotation rate and electrolyte temperature. 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 adsorptive behaviour of gentisic acid follows the Freundlich adsorption isotherm.