The kinetics of Ru (III) catalysed oxidation of diacetone alcohol (DAA) by acid bromate has been studied in aqueous H2SO4 medium and the reaction was found to be first order each in [BrO3 –] and [Ru (III)] and fractional order in [DAA]. The order in [H+] was found to be unity. From the effect of [H+], [KCl], [ClO4 −] and [HOAc] on rate, HBrO3 is established as the reactive species. The products of the oxidation were identified as acetone, acetic acid and formic acid. A mechanism involving a complex formation between DAA and Ru (III) in a fast equilibrium step followed by the oxidation of this complex by Br (V) in a slow step has been proposed.