PURPOSE: To obtain the titled compound having a high purity and a high MW, by centrifuging a solution prepared by dissolving hyaluronic acid (sodium salt) in brine so that part of the accompanying impurities in said acid may remain undissolved and adding a water-soluble non-solvent to the supernatant.

CONSTITUTION: To an aqueous solution of hyaluronic acid (sodium salt) (A) prepared by treating a ground animal tissue containing hyaluronic acid with a proteolytic enzyme and removing insolubles from the product, 100W150wt%, based on component A, (12W18C) alkyl pyridinium halide (wherein the halogen is Cl, Br or I) (B) is added to precipitate an adduct between components A and B. This precipitate is dissolved in brine (10W50°C) of a concentration of 0.5W 1.5wt% so that most of component A may dissolve but part of the accompanying impurities may disperse in the form of fine particles of insoluble gummy matter. To a supernatant obtained by centrifuging the above-obtained solution, 1.5W 3pts.wt. water-soluble non-solvent (e.g., ethanol) per pt.wt., component A is added to precipitate component A, which is then filtered, washed, and dried to obtain the titled compound.