The anti-corrosive effect of xanthone (XAN) on the corrosion of mild steel in 0.5 M H(2)SO(4) has been studied by gravimetric and UV-visible spectrophotometric methods at 303-333 K. Results obtained revealed that XAN performed excellently as a corrosion inhibitor for mild steel in sulphuric acid solution. Inhibition efficiency increases with increase in concentration of XAN but decreases with rise in temperature which is suggestive of physical adsorption mechanism although chemisorption may also play a part. Dubinin-Radushkevich adsorption isotherm model was found to adequately describe the adsorption of XAN onto the mild steel surface. Kinetic parameters of activation and thermodynamic parameters using the statistical model were calculated and discussed. The corrosion process in 0.5 M H(2)SO(4) in the absence and presence of XAN follows first-order kinetics. The UV-visible absorption spectra of the solution containing the inhibitor after the immersion of mild steel specimen indicate the formation of a XAN-Fe complex. Quantum chemical calculations have been performed using DFT and several quantum chemical indices were calculated and correlated with the inhibitive effect. (C) 2010 Elsevier B.V. All rights reserved.