The reaction between enneamolybdomanganate(IV) and glutathione is studied under second‐order conditions in aqueous perchloric acid. The reaction first‐order in both the reactants and initiated through formation of a precursor complex. Protonated forms of both the reactants are found to be active as evidenced by the accelerating effect of increasing hydrogen ion concentration effect. The second step of the reaction is the slow decomposition of the complex leading to the formation of hydroxyl intermediate. The final product glutathione disulfide is formed in the fast third step as a result of reaction of intermediate with another glutathione cation.