[en] The reaction of the cobalt(III)--polyamine complexes [Co(en)₃]³⁺, [Co(dien)₂]³⁺, [CoCl₂(trien)]⁺ (en = ethylenediamine, dien = diethylenetriamine, trien = triethylenetetramine) with OH radicals have been investigated by conductometric pulse radiolysis in weak acid solutions. All complexes react with OH with k = (3.0 +- 0.2) x 10⁸M^-1s^-1. The ligands are oxidized and the Co(III) is reduced to Co(II) by the oxidized ligands. The dissociation rates of the degraded and undegraded ligands are measured, and the rate constant for all complexes examined are shown to increase with increasing hydrogen ion concentration. The primary oxidation mechanisms of these complexes are discussed. 6 figures, 1 table