The oxidation of an essential amino acid like lysine by nicotinium dichromate in aqueous medium in the presence of perchloric acid was studied. The reaction was first order with respect to oxidant, fractional order with respect to substrate and second order with respect to perchloric acid. The increase in ionic strength had negligible effect on the rate. Amino acid was converted to the corresponding carbonyl compound. No polymerisation was observed with acrylonitrile. The addition of Mn2+ ion had a noticeable catalytic effect on the rate. The rates were determined at four different temperatures and the thermodynamic parameters were evaluated.