Postgraduate and Research Department of Chemistry, National College, Trichy-620 001, Tamilnadu, India E-mail : lathaa_ramesh@yahoo.com Fax : 91-431-2482995 Manuscript received 22 December 2008, revised 4 February 2009, accepted 5 February 2009 The kinetics of oxidation of valine, leucine, isoleucine and phenylalanine by N-Bromonicotinamide (NBN) in acetic acid-water in presence of hydrochloric acid has been studied. The reaction shows inverse order dependence on oxidant and [H+]. Increase in [amino acid) has a slight positive effect on the rate, Indicating fractional order dependence. Addition of salts like K2SO4, Na2SO4, KCl to the reaction medium has no effect on the rate. Increase in temperature increases the rate of the reaction. The activition parameters have been computed. A mechanism consistent with the results has been proposed.