The corrosion behaviour of steel at various concentrations of perchloric acid was studied by weight loss method in temperature range from 298 to 323 K. Results obtained show that corrosiveness of acid increases with its concentration and temperature. The logarithm of corrosion rate was plotted against the acid concentration and values of Hammett H-0 and Strehlow R-0(H) acidity functions. The activation energies, enthalpies and entropies of the corrosion process of steel were also determined and fitted against R-0(H). (C) 2009 Elsevier B.V. All rights reserved.