PREPARATION OF CARBOXYPOLYSACCHARIDE

PROBLEM TO BE SOLVED: To provide a method for effectively separating a ruthenium compound from a reaction mixture in preparing a carboxypolysaccharide polymer with an oxidizing agent using the ruthenium compound. SOLUTION: A method for oxidizing a polysaccharide by a combination of a ruthenium compound and an oxidizing agent to prepare a carboxypolysaccharide which comprises (1) adding an oxidizing agent to a mixed solution after reaction to render ruthenium in a higher oxidation state, (2) extracting the ruthenium with a water-insoluble organic solvent, (3) extracting the ruthenium from the organic solvent with an acidic solution, and (4) reusing the recovered ruthenium in the oxidation of a polysaccharide. A reducing agent is added in the organic solvent in step (3), and the reducing agent to be used is at least one member selected from a sulfite salt, hydrazine and its salt, hydroxylamine and its salt, hydrogen peroxide, a quinone, methanol, ethanol and 2-propanol.