The Kinetics of Oxidation of amino acids glycine, alanine and valine by manganese (III) acetate in aqueous sulphuric acid has been studies. The reaction is found to proceed through the formation of intermediate complex. This shows an inverse dependence on [H2SO4]. The reaction has second order dependence with respect to Mn (III) and first order dependence with respect to substrate. The mechanism consistent with rate data has been proposed.