The oxidation of L-Leucine by alkaline diperiodatoargentate(III) (DPA) at 298 K and a constant ionic strength of 1.0 mol dm(-3) was studied spectrophotometrically. The oxidation products are pentanoic acid and Ag (I). The stoichiometry is [L-Leucine]:[DPA] 1:2. The reaction is of first order in [DPA] and has less than unit order in both [L-Leucine] and [alkali] and a retarding effect in [IO4-]. The oxidation reaction in alkaline medium has been identified.