2,3-Diketocarboxymethylcellulose was prepared by the oxidation of carboxymethylcellulose (CMC) with potassium permanganate in alkaline solutions (pH greater than or equal to 12) with a yield of 98.1%. IR spectroscopy and microanalysis have elucidated the chemical structure of the synthesized macromolecule (CMCK). A tentative reaction mechanism for oxidation is suggested.