The oxidation of sensitive sulphide located in a biomolecule such as methionine residue in a peptide or protein, the redox reaction is affected by amino and carboxyl groups present in close proximity to sulphide function. Because of its susceptibility to oxidation, methionine (Met) is thought to play a key role in the migration of unpaired electron in peptides and proteins. By choosing oxo (salen) chromium (V) ion as suitable biomimics for the peptide complexes that are formed during the reduction of Cr (VI) with biological reductants, the oxidation of methionine and ethionine with this in aqueous medium has been investigated by spectrophotometric method. The presence of water facilitates ligation of water to the Cr centre and forms an active oxidant [H2O - (salen) Cr=O] + .The reaction is found to be first order each in the oxidant and the substrate. The presence of H+ ions accelerates the reaction rate. It is found to be first order with respect to H+ ion. The second order rate constant increases with increase in the water content in the reaction medium. The reaction is carried out at different temperatures and activation parameters are calculated. From the kinetic data and stoichiometric analysis, a mechanism involving direct oxygen transfer from oxidant [H2O-(salen) Cr=O] + to the substrate has been proposed as a suitable mechanism for the reaction.