Kinetics of oxidation of L-proline by hexacyanoferrate(III) catalyzed by osmium(VIII) in alkaline medium was studied at 30 degrees C. A mechanism involving free radical path was proposed. Rate law of the reaction was derived as rate = kK(1)K(2)[HCF][L-proline][OH-][Os(VIII)]/1 + K-1[OH-] + K1K2[L-proline][OH-] The rate constant k and equilibrium constants K-1 and K-2 were evaluated as 3.79 x 10(3) dm(3) mol(-1) s(-1), 0.52 dm(3) mol(-1), and 3.78 x 10(3) dm(3) mol(-1), respectively, The main reactive species of the catalyst appears to be OsO5(OH)(3-). The oxidative product Of L-proline was identified as L-glutamic acid which is different from the earlier reports. The literature reveals that 4-amino butyric acid, 4-amino butaraldehyde and keto acids were the oxidative products. Activation parameters were evaluated as E-a = 33.5 +/- 2 kJ mol(-1), Delta H double dagger = 31.0 +/- 0.2 kJ mol(-1), Delta S double dagger = -24 +/- 1.5 J K-1 mol(-1), Delta G double dagger = 38.0 +/- 2 kJ mol(-1).