The kinetics of oxidation of kappa-carrageenan (KCAR) as a sulfated polysaccharide by cerium(IV) in aqueous perchlorate solutions at a constant ionic strength of 2.0 moldm−3 have been investigated, spectrophotometically. The results showed a first-order dependence in [CeIV] and fractional-first-order kinetics in carrageenan concentration. A kinetic evidence for the formation of 1:1 complex has been revealed. The hydrogen ion dependence of the reaction rate indicated that the oxidation process is acid catalyzed. The oxidation product was identified by the spectral data and elemental analysis. The activation and thermodynamic parameters have been evaluated and a relevant reaction mechanism is suggested and discussed.