The leaching of goethite in solutions of perchloric, sulphuric, and hydrochloric acids and in perchloric acid in presence of sulphur dioxide has been investigated. Suspensions of goethite powder (-65, +150 mesh) were leached over a wide range of temperatures, acid concentrations and sulphur dioxide pressures. Strong solutions of hydrochloric acid leached goethite powder more rapidly than equivalent solutions of sulphuric acid, whilst at low concentrations sulphuric acid was the more active reagent. Perchloric acid was found to leach the mineral only very slowly. The rate of dissolution was found to increase with time in the early stages of leaching with all concentrations of sulphuric acid, with strong solutions of hydrochloric acid, and with perchloric acid solutions containing sulphur dioxide. This phenomenon has been correlated with changes in the surface morphology of the goethite during leaching. The rate data derived from the observed results have enabled the effects of temperature, acid type, concentration and partial pressure of sulphur dioxide on rate of leaching to be studied. A common mechanism of leaching is proposed in which protonation of the hydrated oxide surface is followed by adsorption of an anion and desorption of the ferric-anion complex.