Oxidation of Leucine by pyridinium chlorochromate in aqueous DMF medium, containing perchloric acid has been studied at 40ºC. The rate of reaction was found to be of first order dependence on [PCC], [Leucine] and [H+]. The increase in the rate of oxidation with increase in acidity indicates the involvement of a protonated chromium (VI) species in the rate-determining step. The product of oxidation has been identified as 2-methylbutanal. The rate of reaction decreased with increase in the polarity (dielectric constant of medium) of solvent, which indicates that there is involvement of an ion–dipole type of interaction in the rate-determining step. The activation parameters have been evaluated. On the basis of the experimental findings, a suitable mechanism has been proposed.