tThe kinetics and mechanism of oxidation of alginate polysaccharide (Alg) by alkaline hexacyanoferrate(III)in basic solutions at a constant ionic strength of 1.0 mol dm−3have been investigated spectrophotomet-rically. The experimental results showed complex kinetics, where the reaction time curves of the pseudofirst-order plots were found to be of sigmoidal S-shape nature. The initial parts of the plots were relativelyfast, followed by slow-linear portions after short time periods. The oxidation rates were increased withincreasing the alkali concentration indicating that the oxidation is base-catalyzed. A kinetic evidence forformation of 1:1 intermediate complexes was revealed. The activation parameters have been evaluatedand a tentative reaction mechanism consistent with the kinetic results is suggested and discussed.