Kinetics of oxidation of L-proline by hexacyanoferrate(III) catalyzed by osmium(VIII) in alkaline medium was studied at 30°C. A mechanism involving free radical path was proposed. Rate law of the reaction was derived asThe rate constant k and equilibrium constants K 1 and K 2 were evaluated as 3.79 × 10 3 dm 3 mol -1 s -1 , 0.52 dm 3 mol -1 , and 3.78 × 10 3 dm 3 mol -1 , respectively. The main reactive species of the catalyst appears to be OsO 5 (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 , ∆H q ) 31.0 ( 0.2 kJ mol -1 , ∆S q ) -24 ( 1.5 J K -1 mol -1 , ∆G q ) 38.0 ( 2 kJ mol -1 .