To impart hyaluronic acid made hardly water soluble obtained without using a chemical crosslinking agent or a chemical modifying agent, with solubility in water in a degree as required for its use or with retainability in tissues, and to use the hardly water soluble hyaluronic acid, controlled in its solubility, as medical materials such as an adhesion preventing material, a wound covering material, a material for injection into the joint, and a tissue replacement type living tissue repairing material.

This is a solubility controlling method wherein the duration of frozen time is controlled in a process of obtaining the hyaluronic acid made hardly water soluble by freezing an aqueous solution of usual hyaluronic acid having pH ≤2.0 followed by its thawing.