Spectrophotometric detection of the formation of short-lived hypomanganate(V), ½KCAR–MnVO4 3, and manganate(VI), ½KCAR–MnVIO4 2, intermediates has been confirmed through the oxidation of K-carrageenan (KCAR) by potassium permanganate in alkaline solutions of pH’s P12 using a conventional spectrophotometer. The short-lived transient species were characterized and a mechanism consistent with experimental observations is suggested.