The kinetics of oxidation of vanillin (VAN) by diperiodatoargentate (III) (DPA) in alkaline medium at a constant ionic strength of 1.0 mol dm(-3) was studied spectrophotometrically. The reaction between DPA and vanillin in alkaline medium exhibits 1:1 stoichiometry (vanillin:DPA). The reaction is first order in [DPA] and has less than unit order both in [VAN] and [alkali]. A decrease in the dielectric constant of the medium increases the reaction rate. An increase in periodate concentration has no effect on the rate. The oxidation reaction in alkaline medium has been shown to proceed via a DPA-vanillin complex, which decomposes slowly in a rate-determining step to give the products. The main products were identified by spot test, IR, and MS studies. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed. Thermodynamic quantities are also determined.