The inhibitive effects of tannic acid and its acid hydrolysis products, gallic acid and glucose, on the corrosion of copper are reported. Under the conditions employed none shows inhibition in hydrochloric acid medium. In nitric acid solution tannic and gallic acids show substantial inhibitive efficiency while glucose has only a very slight effect. It is proposed that gallic acid acts as a cathodic inhibitor which modifies the corrosive environment while tannic acid behaves both as a cathodic and anodic inhibitor due to the formation of an oxidation product adsorbed on the copper surface. X-ray diffraction and attenuated total reflectance spectroscopy are invoked to identify the corrosion products and the nature of the adsorbed species. -- AATA