The kinetics of iridium(III)-catalyzed oxidation of sulphanilic acid by diperiodatocuprate(III) (DPC) in alkaline medium at a constant ionic strength of 0.50 mol dm(-3) was studied spectrophotometrically. In the presence of iridium(III), the reaction between sulphanilic acid and DPC in alkaline medium exhibits 1:4 stoichiometry (sulphanilic acid: DPC). The reaction shows first order dependence on [DPC] and [iridium(III)], and less than first order both in [sulphanilic acid] and [alkali]. Active species of the catalyst and oxidant have been identified. The main products were identified by IR and spot tests. The probable mechanism was proposed and discussed. The reaction constants involved in the different steps of the mechanism were evaluated. The activation parameters with respect to the slow step of the mechanism were computed and discussed.