The kinetics of oxidation of lysine with chromium (VI) has been studied in perchloric acid medium. The oxidation product was identified as chromium (III) and 5-aminopentanaldehyde. The reaction is first order with respect to chromium (VI) and less than unit order in lysine concentration. Increase in acid concentration accelerates the reaction rate. Ionic strength and added products did not have any significant effect on the reaction. A suitable mechanism is proposed and reaction constants have been evaluated. Activation parameters have also been calculated.