The anodic dissolution and partial passivation of tin in 4.5–8 M sulphuric acid solutions has been studied using rotating ring—disk voltammetry. In the region of active dissolution a Tafel slope of 1/(30 ± 3) mV−1 was measured. This value was found to be independent of acid concentration. A reaction mechanism is presented to explain this slope. It was found that tin dissolves both in the active and partly passive potential region in the form of bivalent tin. Oxidation to the tetravalent state seems to occur only at high anodic potentials. Oxygen evolution starts only at potentials above 3 V (vs. Hg2SO4/Hg). Analysis of the passivating film formed on the electrode surface using SEM, XRD, XPS and SIMS showed that the film is mainly tin oxide, SnO, mostly in an amorphic form.